CN110433766A - A kind of modified mesoporous silicon fiml and its preparation method and application greatly of lanthanum - Google Patents

Abstract

The invention belongs to the field of material preparation technology and separation technology, and relates to a preparation method of a lanthanum-modified large mesoporous silicon membrane and an application of phosphorus adsorption in water bodies. The present invention uses natural biomass cellulose nanocrystals as a template, tetramethoxysilane as a silicon source, and adopts a solvent volatilization self-assembly method to prepare a CNCs/silicon dioxide composite film, and then removes the CNCs template by an acid washing method to form a large mesoporous Silicon oxide film, and then lanthanum is modified on the surface of the large mesoporous silicon film by ethanol evaporation followed by calcination. The phosphoric acid in the water body is adsorbed by the oscillation method, which has excellent adsorption performance. Advantages of the present invention: the lanthanum-modified large mesoporous silicon membrane is obtained by a simple preparation method. Because the mesoporous structure is relatively large, about 20 nm, it is beneficial to the later surface modification, and it is not easy to cause mesopore blockage, and has a larger lanthanum loading capacity, thereby It has a large adsorption capacity, and the material is green and environmentally friendly. Compared with powder materials, membrane adsorbents are recyclable and easy to reuse.

Description

A kind of lanthanum modified large mesoporous silicon film and its preparation method and application

technical field

The invention belongs to the technical field of material preparation and separation, and relates to a method for preparing a lanthanum-modified large mesoporous silicon membrane, in particular to a method for preparing a novel adsorbent used for water pollution treatment, and phosphoric acid used in adsorption and separation of water bodies root ion.

Background technique

Although the earth is rich in water resources, about 70% of the earth is covered by water, but fresh water resources are quite scarce, accounting for 2.53% of the global total water. The normal life of our human beings is also inseparable from the demand for fresh water. However, with the development of industry and the improvement of people's living standards in recent years, a large amount of untreated industrial wastewater and urban sewage have been discharged into water bodies, causing very serious water pollution problems. In particular, a large amount of phosphorus-containing wastewater is discharged into the water body, resulting in eutrophication of the water body. The eutrophication of the water body leads to the decline of water quality, the death of aquatic organisms, and the stench of corpses, which destroys the natural environment where we live, affects our daily life, and causes considerable waste of resources. The previous literature studied the eutrophication degree of 22 typical lakes in the Great Lakes region of the country, and the research results showed that during 2010-2011, 59.1% of the typical lakes were in different degrees of eutrophication. The problem of eutrophication in water body mainly comes from the high content of nitrogen and phosphorus elements in water body. If the content of phosphorus in water body exceeds 0.023mg/L, it will easily lead to eutrophication of water body. Eutrophication of water body has considerable influence on environment, agriculture, fishery and even public life. It will lead to overgrowth of algae and plankton, reduce the oxygen content of the water body, kill a large number of fish, and affect the economic income of fishermen. And fish death and corruption produce stench, also can seriously damage the environment that people live. The drinking water of the citizens will also be affected by it, and the purification procedures of the water plant will be increased, and it is difficult to purify it. Therefore, it is very necessary to study a material that absorbs phosphorus in water to purify water quality.

Nowadays, there are many research reports on related water treatment technologies, such as biological methods, chemical precipitation methods, crystallization and adsorption methods, which can be applied to the removal of phosphoric acid, but these methods have many limitations. For example, biological methods require many specific environmental factors; chemical precipitation methods are easy to cause secondary pollution; crystallization methods are difficult to recycle, etc. In contrast, the use of adsorption and separation technology for phosphoric acid adsorption in water has many advantages, such as wide application range, good recovery and reusability, and good effect of adsorbent on water treatment, making it a phosphoric acid with great application prospects. Approach.

Mesoporous silicon materials are commonly used adsorbents in adsorption methods. Among them, mesoporous silicon materials have certain advantages. Mesoporous silicon dioxide membrane materials show excellent adsorption performance due to their large specific surface area and a large number of mesoporous structures. It can be applied to adsorb phosphorus in water. The pure mesoporous silica membrane material does not have a large adsorption capacity for phosphorus, but its adsorption performance can be greatly increased after modification with lanthanum. However, the current mesoporous silica membrane material has a small pore size, poor adsorption performance, and slow adsorption speed.

Contents of the invention

The invention is a method for preparing a lanthanum-modified large mesoporous silicon membrane with a large adsorption capacity for phosphate ions. Cellulose nanocrystals (CNCs) are used as a template and tetramethylorthosilicate (TMOS) is used as a silicon source. , after removing the template by pickling, the large mesoporous silicon membrane material can be synthesized, which can be used as an adsorption material for the separation of phosphate. The materials used in the preparation of the invention are green and cheap, and belong to environment-friendly materials, and the preparation method is simple and has remarkable economic benefits.

The experimentally obtained mesoporous silica film has a chiral liquid crystal nematic structure and exhibits bright iridescent colors. The obtained membrane material has a large mesoporous structure, which is conducive to the rapid adsorption and separation of phosphorus in water, and the active sites of lanthanum are beneficial to the selective adsorption and separation of phosphorus.

A preparation method of lanthanum modified large mesoporous silicon membrane, the steps are as follows:

Step 1: Prepare cellulose nanocrystalline CNCs by hydrolyzing medical absorbent cotton with sulfuric acid, and set aside;

Step 2: ultrasonically treat the cellulose nanocrystals prepared in step 1, add a certain amount of anhydrous glucose, and then place it on a magnetic stirrer to mix it evenly, then add the silicon precursor tetramethyl orthosilicate TMOS and continue stirring Hydrolyze, pour into a polytetrafluoroethylene petri dish, dry in a water bath to form a film, and obtain a cellulose nanocrystal/silicon dioxide composite film A; Step 3: Composite the cellulose nanocrystal/silicon dioxide obtained in step 2 Membrane A is placed in a sulfuric acid solution to remove the cellulose nanocrystal template to obtain a large mesoporous silicon membrane B;

Step 4: Put the large mesoporous silicon membrane B obtained in step 3 in a beaker, then add a mixed solution of lanthanum nitrate hexahydrate and ethanol, and use the ethanol evaporation method to modify the silicon membrane in a water bath oscillator, and finally place it in an oven to obtain Modified large mesoporous silicon membrane C;

Step 5: Calcining the modified large mesoporous silicon membrane C obtained in step 4 in a muffle furnace to obtain the final product lanthanum modified large mesoporous silicon membrane D.

In step 1, the step of preparing cellulose nanocrystalline CNCs is: placing medical absorbent cotton in 40-60 wt% sulfuric acid solution, stirring and hydrolyzing at 35-55°C for 1-3 hours, and then diluting with a large amount of ultrapure water to inhibit the hydrolysis of cellulose ; Stand overnight for stratification, pour off the supernatant, centrifuge and wash the cellulose nanocrystal dispersion; transfer the white suspension after centrifugation to a dialysis membrane for dialysis, and the molecular weight cut-off of the dialysis membrane is 11000 ～15000, the dialysis time is 1～5 days; until the pH value is equal to 2.4, dilute and sonicate to obtain a cellulose nanocrystal suspension with a mass percent concentration of 3%～5%.

In step 2, the dosage ratio of the cellulose nanocrystals, anhydrous glucose and tetramethyl orthosilicate is 10-20 mL:100-200 mg:400-1000 μL. The ultrasonic time is 10-30min; the stirring temperature after adding glucose is 20-30°C, and the time is 0.5-1.5h; the stirring temperature after adding tetramethyl orthosilicate is 20-30°C, and the time is 2-2 3h. The drying and film forming process is as follows: in a polytetrafluoroethylene petri dish, drying in a water bath at 20-30° C. for 2-7 days.

In step 3, the process of removing the cellulose nanocrystal template in the sulfuric acid solution is as follows: bathing the cellulose nanocrystal/silicon dioxide composite film A in the sulfuric acid solution for 5 to 15 days, the concentrated sulfuric acid and water in the sulfuric acid solution The volume ratio of the water bath is 1:4~1:2, and the temperature of the water bath is controlled at 70~90°C.

In step 4, the dosage ratio of the large mesoporous silicon membrane B, ethanol, and lanthanum nitrate hexahydrate is 1g:50-200mL:0.3-6g, the temperature of the water bath is 40-80°C, and the shaking time is 12-36h. Dry in an oven, and the temperature of the oven is controlled at 60-100°C.

In step 5, the obtained modified large mesoporous silicon membrane C is placed in a muffle furnace, initially heated to 100°C at 5-10°C·min ^-1 , kept for 1-3h, and then heated at 5-10°C·min ^- 1 ^1. Raise the temperature to 500-600° C. and keep it for 5-8 hours to obtain the final product D of lanthanum-modified large mesoporous silicon membrane.

The lanthanum-modified large mesoporous silicon membrane prepared by the invention is used for adsorbing and separating phosphate radicals in water bodies.

The cellulose nanocrystals (CNCs) described in the present invention are generated by the hydrolysis of medical absorbent cotton, and are a kind of biomass template.

Tetramethylorthosilicate (TMOS) described in the present invention is used as a silicon source to generate a silicon dioxide film substrate.

The glucose described in the present invention is used to prevent cracking and increase the toughness of the membrane.

The lanthanum nitrate hexahydrate described in the present invention is for the purpose of modifying the large mesoporous silicon membrane material for selective adsorption and separation of phosphorus.

The above-mentioned lanthanum-modified large mesoporous silicon membrane is applied to absorb phosphate ions in water bodies, and the specific method is carried out according to the following steps:

(1) Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Accurately weigh 20mg of silicon membrane adsorbent and place it in a 10mL colorimetric tube, adjust the pH value of the solution to range from 2.0 to 11.0 with hydrochloric acid and sodium hydroxide, shake in a constant temperature air bath at 25°C for 24 hours during the adsorption process, and then The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated.

(2) Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Add 20mg of membrane material adsorbent to a 10mL colorimetric tube, and calibrate to 10mL with pH=4 phosphoric acid solution. Place in a constant temperature air bath and shake for 24 hours, set the temperature at 20 to 40°C, take the supernatant and use an inductively coupled plasma spectrometer to determine the final concentration of the phosphoric acid solution, and calculate the adsorption amount.

(3) Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Dilute the standard solution into phosphoric acid solutions with different concentrations (10, 25, 50, 75, 100, 125, 150, 175, 200 mg/L), and adjust the pH of the solution to 4. Weigh 20mg of silicon membrane adsorbent and add it to a 10mL colorimetric tube, calibrate to 10mL with phosphoric acid solutions of different concentrations, place in a constant temperature air bath at 25°C and shake for 24 hours, take the supernatant and use an inductively coupled plasma spectrometer to determine the phosphoric acid solution The final concentration of , and calculate the adsorption amount. If the volume of the mixed solution added is W (L), the initial concentration of the prepared solution is C ₀ (mg/L), and its concentration after a certain period of time is C _t (mg/L), then the adsorption capacity q _t (mg /g) is:

q _t =V(C ₀ -C _t )/W

(4) Weigh 20 mg of membrane material and add it to a 10 mL colorimetric tube, and calibrate to 10 mL with 200 mg/L phosphate solution. Place the colorimetric tube in a constant temperature air bath at 25°C and vibrate for 5, 15, 30, 60, 90, 120, 180, 270, 360, and 720 minutes, and then take the supernatant to determine the final concentration of the phosphoric acid solution through an inductively coupled plasma spectrometer. concentration and calculate the adsorption capacity.

(5) Prepare a series of solutions of phosphate solutions (F ^- , Cl ^- , NO ₃ ^- and SO ₄ ^2- in the form of sodium salts) with coexisting anions using the standard solution (pH = 4, 25°C) to obtain the final The concentration is 150mg/L for each anion. Add 20mg of membrane material into a 10mL colorimetric tube, and calibrate to 10mL with the prepared phosphate solution. The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated.

Technical advantage of the present invention:

(1) The present invention uses biomass cellulose nanocrystals (CNCs) as a template, and uses cellulose that exists in large quantities in nature as the initial preparation material, which is cheap, easy to obtain, and environmentally friendly, and has properties such as high purity, high degree of polymerization, and high crystallinity , high hydrophilicity, high Young's modulus, high strength, ultra-fine structure and high transparency.

(2) The large mesoporous silica membrane after removing the template has a higher specific surface area and a larger mesoporous pore size (20nm), which is conducive to further modification of the material, and the loading of more lanthanum oxide is not easy to cause mesoporous blocking. , which is conducive to the acquisition of higher adsorption capacity, and the large mesoporous structure is conducive to increasing the rate of adsorption, thereby improving the adsorption efficiency.

(3) The present invention uses a two-step method to modify the surface of the mesoporous silicon membrane, and introduces the lanthanum active sites into the mesoporous pores, which can ensure the uniform distribution of the active sites.

(4) Compared with powder materials, the prepared membrane materials have the advantages of easy recycling and reuse.

Description of drawings

Fig. 1 is the scanning electron microscope picture of the large mesoporous silicon film prepared by the present invention;

Fig. 2 is the transmission electron microscope picture of the large mesoporous silicon membrane prepared by the present invention;

Fig. 3 is the Fourier transform infrared transform spectrogram of the modified large mesoporous silicon membrane prepared by the present invention;

Fig. 4 is a diagram showing the influence of the lanthanum-modified mesoporous silicon membrane prepared by the present invention on the adsorption amount of phosphate at different pHs.

Fig. 5 is a diagram showing the adsorption effect of lanthanum-modified mesoporous silicon membranes on phosphate radicals at different times in the present invention.

Fig. 6 is a graph showing the adsorption effect of the lanthanum-modified mesoporous silicon membrane prepared in the present invention in different concentrations of phosphate solutions.

Detailed ways

The present invention will be further described below in conjunction with specific implementation examples.

Example 1

(1) Weigh 10 g of medical absorbent cotton, dissolve it in a sulfuric acid solution with a concentration of 40 wt %, and stir at 35° C. for 3 h. Afterwards, the hydrolyzed cellulose was diluted with 2000 ml of cold ultrapure water to stop the hydrolysis process and allowed to stand for 12 h. Discard the supernatant, and centrifuge the remaining white cellulose. Subsequently, the centrifuged white suspension was washed 3 times with deionized water to remove soluble cellulose material, and then placed in a dialysis bag (molecular weight cut-off 11000-15000) for 2-5 days (until the pH of the suspension = 2.4 ). The finally obtained solid product was diluted in water, and dispersed by ultrasonic treatment for 10 minutes before use, and diluted to a concentration of 3% by mass.

(2) 15 mL of the CNCs suspension (pH=2.4) obtained in step 1 was sonicated for 10 min. 100 mg of anhydrous glucose was added to the CNCs and stirred at 20 °C for 0.5 h, after which 400 μL of tetramethoxysilane (TMOS) was added to the mixture suspension. The mixture suspension was stirred at 20 °C for 1.5 h. Afterwards, the homogeneous mixture was poured into polystyrene Petri dishes (d=90 mm) and dried at room temperature. Evaporate slowly in a water bath at 20°C for 2 to 3 days to form a complete CNCs/silicon dioxide composite film A, referred to as CSF.

(3) Place the cellulose nanocrystal/silicon dioxide composite membrane A obtained in step (2) in a water bath in a sulfuric acid solution for 5 days to obtain a large mesoporous silicon membrane B, referred to as MSF;

Among them, the volume ratio of concentrated sulfuric acid and water in the sulfuric acid solution is 1:4, and the temperature of the water bath is controlled at 80°C.

(4) Add 1 g of the large mesoporous silicon membrane B synthesized in step (3) into a beaker, then add 100 mL of ethanol dissolved with 0.3482 g of lanthanum nitrate hexahydrate into the beaker, and place the beaker in a 40°C water bath for 12 hours. , and then dried in a 60°C oven;

(5) Place the modified mesoporous silicon membrane in step (4) in a muffle furnace, initially raise the temperature to 100°C at 5°C·min ^-1 , keep it for 1h, and then raise the temperature to 500°C at 5°C·min ^-1 ℃ and kept for 5 hours to obtain the final product lanthanum-modified macro-mesoporous silicon film D, referred to as La-MSF-20 (Si/La molar ratio is 20:1).

(6) The lanthanum-modified large mesoporous silicon membrane was tested for optimal adsorption pH.

Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Accurately weigh 20mg of silicon membrane adsorbent and place it in a 10mL colorimetric tube, adjust the pH value of the solution to range from 2.0 to 11.0 with hydrochloric acid and sodium hydroxide, shake in a constant temperature air bath at 25°C for 24 hours during the adsorption process, and then The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated to obtain an optimal pH of 3 or 4.

(7) The lanthanum-modified large mesoporous silicon membrane was tested for optimal adsorption temperature.

Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Add 20mg of membrane material adsorbent to a 10mL colorimetric tube, and calibrate to 10mL with pH=4 phosphoric acid solution. Place in a constant temperature air bath and shake for 24 hours, set the temperature at 20-40°C, take the supernatant and use an inductively coupled plasma spectrometer to determine the final concentration of the phosphoric acid solution, and calculate the adsorption amount.

(8) Evaluate the isotherm adsorption performance of the lanthanum-modified macromesoporous silicon membrane.

Accurately weigh potassium dihydrogen phosphate to prepare a 200mg/L phosphoric acid standard solution. Dilute the standard solution into phosphoric acid solutions with different concentrations (10, 25, 50, 75, 100, 125, 150, 175, 200 mg/L), and adjust the pH of the solution to 4. Weigh 20mg of membrane material and add it to a 10mL colorimetric tube, calibrate to 10mL with phosphoric acid solutions of different concentrations, shake in a constant temperature air bath at 25°C for 24 hours, take the supernatant to determine the concentration of phosphoric acid solution by inductively coupled plasma spectrometer final concentration and calculate the adsorption capacity. If the volume of the mixed solution added is W (L), the initial concentration of the prepared solution is C ₀ (mg/L), and its concentration after a certain period of time is C _t (mg/L), then the adsorption capacity of the membrane q _t (mg/g) is:

q _t =V(C ₀ -C _t )/W

(9) The lanthanum-modified large mesoporous silicon membrane was subjected to a kinetic analysis test.

Accurately weigh 20 mg of membrane material and add it to a 10 mL colorimetric tube, and calibrate to 10 mL with 200 mg/L phosphate solution. Place the colorimetric tube in a constant temperature air bath at 25°C and vibrate for 5, 15, 30, 60, 90, 120, 180, 270, 360, and 720 minutes, and then take the supernatant to determine the final concentration of the phosphoric acid solution through an inductively coupled plasma spectrometer. concentration and calculate the adsorption capacity.

(10) The lanthanum-modified large mesoporous silicon membrane was subjected to the coexistence ion adsorption test.

A series of solutions of phosphate solutions (in the form of sodium salts of F ⁻ , Cl ⁻ , NO ₃ ^- and SO ₄ ^2- ) with coexisting anions were prepared using standard solutions (pH = 4, 25 °C) to obtain a final concentration of Anion 150mg/L. Add 20 mg of film sample into a 10 mL colorimetric tube, and calibrate to 10 mL with the prepared phosphate solution. The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated.

Example 2

(1) Weigh 10 g of medical absorbent cotton, dissolve it in a sulfuric acid solution with a concentration of 50 wt %, and stir at 45° C. for 2 h. Afterwards, the hydrolyzed cellulose was diluted with 2000 ml of cold ultrapure water to stop the hydrolysis process and allowed to stand for 12 h. Discard the supernatant, and centrifuge the remaining white cellulose. Subsequently, the centrifuged white suspension was washed 3 times with deionized water to remove soluble cellulose material, and then placed in a dialysis bag (molecular weight cut-off 11000-15000) for 2-5 days (until the pH of the suspension = 2.4 ). The finally obtained solid product was diluted in water, and dispersed by ultrasonic treatment for 10 minutes before use, and diluted to a concentration of 3.5% by mass.

(2) 15 mL of the CNCs suspension (pH=2.4) obtained in step 1 was sonicated for 10 min. 150 mg of anhydrous glucose was added to the CNCs and stirred at 25 °C for 1 h, after which 600 μL of tetramethoxysilane (TMOS) was added to the mixture suspension. The mixture suspension was stirred at 25 °C for 2 h. Afterwards, the homogeneous mixture was poured into polystyrene Petri dishes (d=90 mm) and dried at room temperature. Evaporate slowly in a water bath at 25°C for 2 to 3 days to form a complete CNCs/silicon dioxide composite film A, referred to as CSF.

(3) placing the cellulose nanocrystal/silicon dioxide composite film obtained in step (2) in a water bath in a sulfuric acid solution for 7 days to obtain a large mesoporous silicon film B, referred to as MSF;

Among them, the volume ratio of concentrated sulfuric acid and water in the sulfuric acid solution is 1:3, and the temperature of the water bath is controlled at 85°C.

(4) Add 1 g of the large mesoporous silicon membrane synthesized in step (3) into a beaker, then add 100 mL of ethanol dissolved with 0.6964 g of lanthanum nitrate hexahydrate into the beaker, place the beaker in a 60°C water bath and shake for 24 hours, Then dry in an oven at 80°C;

(5) Place the modified mesoporous silicon membrane in step (4) in a muffle furnace, initially raise the temperature to 100°C at 10°C·min ^-1 , keep it for 2 hours, and then raise the temperature to 550°C at 10°C·min ^-1 ℃ and kept for 6 hours to obtain the final product lanthanum-modified macro-mesoporous silicon film D, referred to as La-MSF-10 (Si/La molar ratio is 10:1).

(6) The lanthanum-modified large mesoporous silicon membrane was tested for optimal adsorption pH.

Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Accurately weigh 20mg of silicon membrane adsorbent and place it in a 10mL colorimetric tube, adjust the pH value of the solution to range from 2.0 to 11.0 with hydrochloric acid and sodium hydroxide, shake in a constant temperature air bath at 25°C for 24 hours during the adsorption process, and then The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated to obtain an optimal pH of 3 or 4.

(7) The lanthanum-modified large mesoporous silicon membrane was tested for optimal adsorption temperature.

Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Add 20mg of membrane material adsorbent to a 10mL colorimetric tube, and calibrate to 10mL with pH=4 phosphoric acid solution. Place in a constant temperature air bath and shake for 24 hours, set the temperature at 20-40°C, take the supernatant and use an inductively coupled plasma spectrometer to determine the final concentration of the phosphoric acid solution, and calculate the adsorption amount.

(8) Evaluate the isotherm adsorption performance of the lanthanum-modified macromesoporous silicon membrane.

Accurately weigh potassium dihydrogen phosphate to prepare a 200mg/L phosphoric acid standard solution. Dilute the standard solution into phosphoric acid solutions with different concentrations (10, 25, 50, 75, 100, 125, 150, 175, 200 mg/L), and adjust the pH of the solution to 4. Weigh 20mg of the membrane material and add it to a 10mL colorimetric tube, calibrate it to 10mL with phosphoric acid solutions of different concentrations, shake it in a constant temperature air bath at 25°C for 24 hours, take the supernatant and use an inductively coupled plasma spectrometer to determine the concentration of the phosphoric acid solution. final concentration and calculate the adsorption capacity. If the volume of the mixed solution added is W (L), the initial concentration of the prepared solution is C ₀ (mg/L), and its concentration after a certain period of time is C _t (mg/L), then the adsorption capacity of the membrane q _t (mg/g) is:

q _t =V(C ₀ -C _t )/W

(9) The lanthanum-modified large mesoporous silicon membrane was subjected to a kinetic analysis test.

Accurately weigh 20 mg of membrane material and add it to a 10 mL colorimetric tube, and calibrate to 10 mL with 200 mg/L phosphate solution. Place the colorimetric tube in a constant temperature air bath at 25°C and vibrate for 5, 15, 30, 60, 90, 120, 180, 270, 360, and 720 minutes, and then take the supernatant to determine the final concentration of the phosphoric acid solution through an inductively coupled plasma spectrometer. concentration and calculate the adsorption capacity.

(10) The lanthanum-modified large mesoporous silicon membrane was subjected to the coexistence ion adsorption test.

A series of solutions of phosphate solutions (in the form of sodium salts of F ⁻ , Cl ⁻ , NO ₃ ^- and SO ₄ ^2- ) with coexisting anions were prepared using standard solutions (pH = 4, 25 °C) to obtain a final concentration of Anion 150mg/L. Add 20 mg of film sample into a 10 mL colorimetric tube, and calibrate to 10 mL with the prepared phosphate solution. The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated.

Example 3

(1) Weigh 10 g of medical absorbent cotton, dissolve it in a sulfuric acid solution with a concentration of 60 wt %, and stir at 50° C. for 1.5 h. Afterwards, the hydrolyzed cellulose was diluted with 2000 ml of cold ultrapure water to stop the hydrolysis process and allowed to stand for 12 h. Discard the supernatant, and centrifuge the remaining white cellulose. Subsequently, the centrifuged white suspension was washed 3 times with deionized water to remove soluble cellulose material, and then placed in a dialysis bag (molecular weight cut-off 11000-15000) for 2-5 days (until the pH of the suspension = 2.4 ). The finally obtained solid product was diluted in water, and dispersed by ultrasonic treatment for 10 minutes before use, and diluted to a concentration of 4% by mass.

(2) 15 mL of the CNCs suspension (pH=2.4) obtained in step 1 was sonicated for 30 min. 200 mg of anhydrous glucose was added to the CNCs and stirred at 30 °C for 1.5 h, after which 800 μL of tetramethoxysilane (TMOS) was added to the mixture suspension. The mixture suspension was stirred at 30 °C for 3 h. Afterwards, the homogeneous mixture was poured into polystyrene Petri dishes (d=90 mm) and dried at room temperature. Slowly evaporate in a water bath at 30°C for 2 to 3 days to form a complete CNCs/silicon dioxide composite film A, referred to as CSF.

(3) Place the cellulose nanocrystal/silicon dioxide composite membrane obtained in step (2) in a water bath in sulfuric acid solution for 11 days to obtain a large mesoporous silicon membrane B, referred to as MSF;

Among them, the volume ratio of concentrated sulfuric acid and water in the sulfuric acid solution is 1:2, and the temperature of the water bath is controlled at 90°C.

(4) Add 1 g of the large mesoporous silicon membrane synthesized in step (3) into a beaker, then add 100 mL of ethanol dissolved with 1.3928 g of lanthanum nitrate hexahydrate into the beaker, place the beaker in a water bath at 80° C. for 36 h, Then dry in an oven at 90°C;

(5) Place the modified mesoporous silicon membrane in step (4) in a muffle furnace, initially raise the temperature to 100°C at 7°C·min ^-1 , keep it for 3h, and then raise the temperature to 600°C at 7°C·min ^-1 ℃, kept for 8 hours, and the final product lanthanum-modified macro-mesoporous silicon film D, referred to as La-MSF-5 (Si/La molar ratio 5:1) was obtained.

(6) The lanthanum-modified large mesoporous silicon membrane was tested for optimal adsorption pH.

Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Accurately weigh 20mg of silicon membrane adsorbent and place it in a 10mL colorimetric tube, adjust the pH value of the solution to range from 2.0 to 11.0 with hydrochloric acid and sodium hydroxide, shake in a constant temperature air bath at 25°C for 24 hours during the adsorption process, and then The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated to obtain an optimal pH of 3 or 4.

(7) The lanthanum-modified large mesoporous silicon membrane was tested for optimal adsorption temperature.

Weigh anhydrous potassium dihydrogen phosphate, prepare phosphoric acid standard solution with ultrapure water, the concentration is 200mg/L. Add 20mg of membrane material adsorbent to a 10mL colorimetric tube, and calibrate to 10mL with pH=4 phosphoric acid solution. Place in a constant temperature air bath and shake for 24 hours, set the temperature at 20-40°C, take the supernatant and use an inductively coupled plasma spectrometer to determine the final concentration of the phosphoric acid solution, and calculate the adsorption amount.

(8) Evaluate the isotherm adsorption performance of the lanthanum-modified macromesoporous silicon membrane.

Accurately weigh potassium dihydrogen phosphate to prepare a 200mg/L phosphoric acid standard solution. Dilute the standard solution into phosphoric acid solutions with different concentrations (10, 25, 50, 75, 100, 125, 150, 175, 200 mg/L), and adjust the pH of the solution to 4. Weigh 20mg of membrane material and add it to a 10mL colorimetric tube, calibrate to 10mL with phosphoric acid solutions of different concentrations, shake in a constant temperature air bath at 25°C for 24 hours, take the supernatant to determine the concentration of phosphoric acid solution by inductively coupled plasma spectrometer final concentration and calculate the adsorption capacity. If the volume of the mixed solution added is W (L), the initial concentration of the prepared solution is C ₀ (mg/L), and its concentration after a certain period of time is C _t (mg/L), then the adsorption capacity of the membrane q _t (mg/g) is:

q _t =V(C ₀ -C _t )/W

(9) The lanthanum-modified large mesoporous silicon membrane was subjected to a kinetic analysis test.

Accurately weigh 20 mg of membrane material and add it to a 10 mL colorimetric tube, and calibrate to 10 mL with 200 mg/L phosphate solution. Place the colorimetric tube in a constant temperature air bath at 25°C and vibrate for 5, 15, 30, 60, 90, 120, 180, 270, 360, and 720 minutes, and then take the supernatant to determine the final concentration of the phosphoric acid solution through an inductively coupled plasma spectrometer. concentration and calculate the adsorption capacity.

(10) The lanthanum-modified large mesoporous silicon membrane was subjected to the coexistence ion adsorption test.

A series of solutions of phosphate solutions (in the form of sodium salts of F ⁻ , Cl ⁻ , NO ₃ ^- and SO ₄ ^2- ) with coexisting anions were prepared using standard solutions (pH = 4, 25 °C) to obtain a final concentration of Anion 150mg/L. Add 20 mg of film sample into a 10 mL colorimetric tube, and calibrate to 10 mL with the prepared phosphate solution. The supernatant was taken to determine the final concentration of the phosphoric acid solution by an inductively coupled plasma spectrometer, and the adsorption amount was calculated.

Fig. 1 is a scanning electron microscope image of a large mesoporous silicon membrane prepared by the present invention: the planar mesoporous structure of the membrane can be seen from the figure.

Fig. 2 is a transmission electron microscope image of the large mesoporous silicon membrane prepared by the present invention: the mesoporous structure of the composite membrane can be seen from the figure.

Fig. 3 is the Fourier transform infrared spectrogram of the material prepared by the present invention: due to the loading of La, the silanol bond at 955cm ^-1 on the surface of the large mesoporous silicon membrane disappears, and the small peak near 1389cm ^-1 is due to the remaining nitrate after calcination.

Fig. 4 is the adsorption capacity diagram of the adsorbent prepared by the present invention at different pHs: it can be seen from the figure that the optimum adsorption pH of the membrane is 4, and the maximum adsorption capacity is about 50 mg/g.

Fig. 5 is the adsorption capacity diagram of the adsorbent prepared by the present invention under different adsorption times; from the figure, we can see that the adsorption rate of the material is very fast in the first 200 minutes, and then the adsorption rate slows down, and reaches the adsorption after about 6 hours balance.

Fig. 6 is a diagram of the adsorption capacity of the adsorbent prepared in the present invention in different concentrations of phosphate, it can be seen that with the increase of the solution concentration, the adsorption capacity gradually increases.

Claims (10)

1. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum, which comprises the steps of:

Step 1: Cellulose nanocrystal CNCs is prepared using sulphuric acid hydrolysis medical absorbent cotton, it is spare；

Step 2: Cellulose nanocrystal prepared by step 1 is ultrasonically treated, and a certain amount of DEXTROSE ANHYDROUS is added, then sets In being allowed to uniformly mixed on magnetic stirring apparatus, the positive quanmethyl silicate TMOS of silicon precursor is added later and continues stirring hydrolysis, pours into In polytetrafluoroethylene (PTFE) culture dish, drying film forming, obtains Cellulose nanocrystal/silica composite films A in a water bath；

Step 3: Cellulose nanocrystal/silica composite films A that step 2 obtains being placed in removal cellulose in sulfuric acid solution and is received Rice crystal template obtains big mesoporous silicon fiml B；Step 4: the big mesoporous silicon fiml B that step 3 is obtained is placed in a beaker, rear that six water are added Lanthanum nitrate and alcohol mixed solution are closed, in water bath chader, using the modified silicon fiml of ethanol evaporation method, is finally placed in baking oven and obtains To modified big mesoporous silicon fiml C；

Step 5: the modification silicon fiml C mesoporous greatly that step 4 obtains being placed in Muffle furnace and is calcined, modified big Jie of final product lanthanum is obtained Hole silicon fiml D.

2. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum as described in claim 1, which is characterized in that in step 1, preparation The step of Cellulose nanocrystal CNCs are as follows: medical absorbent cotton is placed in 40~60wt% sulfuric acid solution, 35~55 DEG C of stirring water 1~3h is solved, the hydrolysis to inhibit cellulose is diluted by a large amount of ultrapure waters；Overnight stand layering, outwells supernatant liquor, to fiber The nanocrystalline dispersion liquid centrifuge separation of element, washing；White suspension after centrifuge separation is transferred in dialysis membrane and is dialysed, it is described The molecular cut off for analysing film is 11000~15000, and dialysis time is 1~5 day；Until pH value is equal to 2.4, dilution, ultrasound is obtained The Cellulose nanocrystal suspension for being 3%~5% to mass percentage concentration.

3. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum as described in claim 1, which is characterized in that described in step 2 Cellulose nanocrystal, DEXTROSE ANHYDROUS, positive quanmethyl silicate amount ratio be the μ of 10~20mL:100~200mg:400~1000 L。

4. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum as described in claim 1, which is characterized in that described in step 2 Ultrasonic time is 10~30min；Whipping temp after the addition glucose is 20~30 DEG C, and the time is 0.5~1.5h；It is described Whipping temp after positive quanmethyl silicate is added dropwise is 20~30 DEG C, and the time is 2~3h.

5. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum as described in claim 1, which is characterized in that described in step 2 Drying film forming are as follows: in polytetrafluoroethylene (PTFE) culture dish, 20~30 DEG C of water-baths are dried 2~7 days.

6. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum as described in claim 1, which is characterized in that described in step 3 In sulfuric acid solution remove Cellulose nanocrystal template process are as follows: by Cellulose nanocrystal/silica composite films A in sulphur The volume ratio of water-bath 5~15 days in acid solution, the concentrated sulfuric acid of sulfuric acid solution and water is 1:4~1:2, bath temperature control 70~ 90℃。

7. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum as described in claim 1, which is characterized in that described in step 4 Big mesoporous silicon fiml B, ethyl alcohol, lanthanum nitrate hexahydrate amount ratio be 1g:50~200mL:0.3~6g, bath temperature be 40~ 80 DEG C, duration of oscillation is 12~36h, is dried in an oven later, and oven temperature is controlled at 60~100 DEG C.

8. a kind of preparation method of the modified big mesoporous silicon fiml of lanthanum as described in claim 1, which is characterized in that in step 5, will To modification silicon fiml C mesoporous greatly be placed in Muffle furnace, initially with 5~10 DEG C of min^-1100 DEG C are warming up to, 1~3h is kept, then exists With 5~10 DEG C of min^-1500~600 DEG C are warming up to, 5~8h is kept, obtains the modified big mesoporous silicon fiml D of final product lanthanum.

9. a kind of modified big mesoporous silicon fiml of lanthanum that the preparation method as described in any one of claim 1~8 obtains, which is characterized in that The mesoporous silicon fiml is chiral liquid crystal nematic structure, has well-regulated big meso-hole structure.

10. a kind of modified big mesoporous silicon fiml of lanthanum as claimed in claim 9 is used for the phosphate anion in selective absorption water body.