Lignin porous microspheres loaded with nano-silver, and preparation method and application thereof
The method of preparing porous silver/lignin nanospheres by O/W/O type composite emulsion suspension crosslinking solves the problems of using toxic chemical reagents and easy agglomeration in the preparation of silver nanomaterials. It achieves efficient dispersion and stability of silver nanospheres, good catalytic activity, and easy recycling, and is suitable for wastewater treatment and photocatalysis.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTH CHINA UNIV OF TECH
- Filing Date
- 2023-03-30
- Publication Date
- 2026-07-07
AI Technical Summary
Existing nano-silver materials use toxic chemical reagents in their preparation process, and are prone to oxidation, agglomeration, and high cost. They are also difficult to recover by centrifugation during application, making it difficult to achieve effective catalytic activity and environmentally friendly recycling.
A nano-silver/lignin composite was prepared by using an O/W/O type composite emulsion suspension crosslinking method, taking advantage of the reducing and dispersing properties of lignin. Porous microspheres were formed by crosslinking agents and chain extenders. Combined with ultrasonic polymerization and oil phase removal, lignin porous microspheres loaded with nano-silver with a particle size of 50-500 μm were prepared.
The nano-silver achieves efficient dispersion and stability. The microspheres have a porous structure, making them easy to recycle and reuse. They also exhibit good catalytic activity and are suitable for applications such as wastewater treatment, photocatalytic degradation, and photocatalytic hydrogen production.
Smart Images
Figure HDA0004153074180000011 
Figure HDA0004153074180000012 
Figure HDA0004153074180000013
Abstract
Description
Technical Field
[0001] This invention belongs to the field of porous microsphere preparation technology, specifically relating to a lignin porous microsphere loaded with silver nanoparticles, its preparation method and application. Background Technology
[0002] In recent years, nanostructured materials have attracted widespread attention due to their chemical, physical, and biological properties and potential applications in many fields, especially metal nanoparticles such as Ag, Au, and Cu, which have been widely used in the field of catalysts. Among them, silver nanoparticles, as a highly efficient catalytic material, have very important applications in wastewater treatment, photocatalytic degradation, and photocatalytic hydrogen production.
[0003] Currently, the main method for preparing nano-silver is chemical reduction, which requires the introduction of large amounts of toxic chemical reagents, thus limiting the development and application of nano-silver. Therefore, selecting a green, environmentally friendly, and renewable reducing agent is of great significance. Furthermore, nano-silver as a catalytic material suffers from a series of drawbacks, including easy oxidation, easy aggregation, and high cost. To address these issues, researchers have proposed the preparation of supported nano-silver catalysts. On the one hand, the dispersion and stabilization effect of the support can solve the problem of nano-silver aggregation and maintain its catalytic activity; on the other hand, it can also solve the problem of nano-silver recycling.
[0004] Among biorenewable polymers, lignin is the third most abundant natural polymer after cellulose and chitosan, and also the most abundant aromatic compound in nature. As one of the three main components of natural lignocellulose raw materials, lignin possesses numerous excellent properties, including abundant availability, environmental friendliness, UV protection, antioxidant properties, antibacterial properties, and biodegradability, making it an ideal material for developing novel polymer composites. Lignin contains a large number of phenolic and alcoholic hydroxyl groups, which give it excellent reducing properties, making it suitable for preparing silver nanoparticles. Furthermore, lignin's three-dimensional network structure and active functional groups provide dispersion, protection, and stabilization for silver nanoparticles. However, currently, silver nanoparticle / lignin composites are either in sol form or can only be dried into powder, facing difficulties in centrifugal recovery during application. Therefore, it is necessary to utilize lignin reduction to prepare silver nanoparticles, and further prepare lignin porous microspheres with a particle size of 50–500 μm loaded with silver nanoparticles. This can effectively improve the catalytic activity of silver nanoparticles and facilitate the recycling of composite materials, which is of great significance for environmental protection, resource recycling, and the development of nanomaterials. Summary of the Invention
[0005] To address the shortcomings and deficiencies of existing technologies for preparing nano-silver / lignin composite materials, the primary objective of this invention is to provide a method for preparing porous lignin microspheres loaded with nano-silver.
[0006] This invention relates to the preparation of lignin porous microspheres loaded with silver nanoparticles based on O / W / O type composite emulsion suspension crosslinking. First, a small-sized and stably dispersed silver nanoparticle / lignin composite is prepared using the reducing and dispersing properties of lignin. Then, an O / W / O type composite emulsion (double emulsion) is prepared using the silver nanoparticle / lignin composite to encapsulate the silver nanoparticle / lignin aqueous solution, forming droplets that crosslink to form regular microspheres. The principle of microsphere pore formation is as follows: On one hand, lignin and chain extenders are connected by a crosslinking agent. The synergistic effect of the crosslinking agent making it easier for lignin molecular chains to form a network structure and the chain extender lengthening the lignin molecular backbone increases the degree of crosslinking of the molecular network and makes the crosslinking points more uniformly distributed, thereby improving the flexibility of the microspheres. Simultaneously, lignin undergoes a certain degree of polymerization and crosslinking under ultrasonic treatment, giving the microspheres both rigidity and flexibility, thus enabling drying and pore formation. On the other hand, an internal oil phase is used as a pore-forming agent. After the internal oil phase, which does not participate in the crosslinking reaction, is removed, larger pores and voids form in its original positions. Therefore, during the drying process, the pores formed by the evaporation of the aqueous phase of the microsphere and the pores formed by the removal of the internal oil phase construct the porous structure of the lignin microsphere.
[0007] Another object of the present invention is to provide lignin porous microspheres loaded with silver nanoparticles prepared by the above preparation method.
[0008] Another object of the present invention is to provide the application of the above-mentioned lignin porous microspheres loaded with silver nanoparticles.
[0009] The objective of this invention is achieved through the following technical solution:
[0010] A method for preparing lignin porous microspheres loaded with silver nanoparticles includes the following steps:
[0011] (1) Add lignin to a silver-containing solution, dissolve it, and then heat it to react to obtain a nano-silver / lignin complex solution;
[0012] (2) Adjust the nano-silver / lignin complex solution to alkalinity and mix it evenly with crosslinking agent and chain extender to obtain nano-silver / lignin aqueous solution;
[0013] (3) Mix the nano-silver / lignin aqueous solution with the inner oil phase containing surfactant and emulsify to obtain an O / W type primary emulsion; then mix the O / W type primary emulsion with the outer oil phase containing surfactant and emulsify to obtain an O / W / O type secondary emulsion.
[0014] (4) After ultrasonic reaction of O / W / O type double emulsion, the oil phase is removed, washed and dried to obtain lignin porous microspheres loaded with silver nanoparticles.
[0015] Preferably, the lignin in step (1) is at least one of sodium lignin sulfonate, sulfonated alkali lignin, carboxylated alkali lignin, aminated alkali lignin, sulfonated solvent-type lignin, carboxylated solvent-type lignin, aminated solvent-type lignin, sulfonated enzymatically hydrolyzed lignin, carboxylated enzymatically hydrolyzed lignin, and aminated enzymatically hydrolyzed lignin.
[0016] Preferably, the silver-containing solution in step (1) is at least one of silver nitrate solution or silver ammonia solution, and the silver content is 1-5 wt%.
[0017] Preferably, the mass ratio of lignin to silver-containing solution in step (1) is 1:2 to 1:5.
[0018] Preferably, the heating reaction in step (1) is carried out at a temperature of 60–80°C.
[0019] Preferably, the heating reaction time in step (1) is 2 to 4 hours.
[0020] Preferably, the alkalinity in step (2) refers to a pH of 10 to 13.
[0021] Preferably, the alkali used in step (2) to adjust the nano-silver / lignin complex solution to alkalinity is at least one of sodium hydroxide and potassium hydroxide.
[0022] Preferably, the crosslinking agent in step (2) is at least one of formaldehyde, glutaraldehyde, glyoxal, epichlorohydrin and N,N-methylenebisacrylamide.
[0023] Preferably, the amount of crosslinking agent used in step (2) is 30-50% of the lignin quality.
[0024] Preferably, the chain extender in step (2) is at least one of ethylenediamine, hexamethylenediamine, polyetheramine, polyethyleneimine, triethylenetetramine, and diethylenetriamine.
[0025] Preferably, the amount of chain extender used in step (2) is 0.1% to 15% of the lignin quality.
[0026] Preferably, the inner oil phase containing surfactant in step (3) consists of surfactant and oil phase, wherein the surfactant accounts for 0.1 to 2% of the total mass of the inner oil phase.
[0027] Preferably, in the inner oil phase containing surfactant in step (3), the surfactant is at least one of Tween-80, sucrose ester, polyethylene glycol, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate; and the oil phase is at least one of toluene, isoamyl alcohol, n-heptane, and ethyl acetate.
[0028] Preferably, the mass ratio of the nano-silver / lignin aqueous solution and the internal oil phase containing surfactant in step (3) is 2:1 to 5:1.
[0029] Preferably, the external oil phase containing surfactant in step (3) is composed of surfactant and oil phase, wherein the surfactant accounts for 2 to 6% of the total mass of the external oil phase.
[0030] Preferably, in the external oil phase containing surfactant in step (3), the surfactant is at least one of Span-60, glyceryl monostearate, calcium stearate and dodecylphenol polyoxyethylene ether; and the oil phase is at least one of cyclohexane, xylene, n-hexane and liquid paraffin.
[0031] Preferably, the mass ratio of the O / W type primary emulsion and the external oil phase containing the surfactant in step (3) is 1:3 to 1:5.
[0032] Preferably, the emulsification conditions for the O / W type colostrum in step (3) are: shearing at 3000-6000 rpm for 10-15 min.
[0033] Preferably, the emulsification conditions for the O / W / O type double emulsion in step (3) are: shearing at 200-300 rpm for 25-40 min.
[0034] Preferably, the ultrasonic power of the ultrasonic reaction in step (4) is 150 to 300 W.
[0035] Preferably, the ultrasonic reaction time in step (4) is 30 to 60 minutes.
[0036] Preferably, the method for removing the oil phase in step (4) is as follows: let it stand at normal pressure for 10 to 30 minutes, and then pour out the upper oil phase.
[0037] Preferably, the washing in step (4) is as follows: first wash with petroleum ether 3 to 6 times, then transfer the microspheres to a Soxhlet extractor and extract with ethanol for 12 to 24 hours.
[0038] Preferably, the drying in step (4) is: freeze drying at -40 to -10°C for 48 to 72 hours or drying at 30 to 70°C under a vacuum of 76 to 90 Pa for 48 to 72 hours.
[0039] The above preparation method yields a lignin porous microsphere loaded with silver nanoparticles.
[0040] The lignin porous microspheres loaded with silver nanoparticles prepared in this invention have a particle size of 50–500 μm.
[0041] The above-mentioned application of lignin porous microspheres loaded with silver nanoparticles as catalysts in oxidation, reduction, and CC coupling reactions.
[0042] The applications of this catalyst in catalytic oxidation, reduction, and CC coupling reactions include wastewater treatment, photocatalytic degradation, and photocatalytic hydrogen production.
[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0044] 1. This invention uses green, environmentally friendly, and renewable lignin as a reducing agent to efficiently prepare nano-silver in an aqueous phase. At the same time, lignin has a certain dispersing and stabilizing effect on nano-silver.
[0045] 2. This invention employs ultrasound-assisted polymerization. Under the action of ultrasound, lignin undergoes a certain degree of polymerization, increasing its molecular weight and improving the cross-linking strength of the microspheres. Simultaneously, the cross-linking agent connects the lignin with the chain extender, giving the microspheres a certain degree of flexibility, which helps prevent the spheres from collapsing after drying and allows them to form a network. Experiments show that without the addition of a chain extender, or when the amounts of the cross-linking agent and chain extender are not within the limits specified in this invention, it is impossible to obtain well-structured, regular lignin microspheres with a porous structure; the product may even be blocky.
[0046] 3. The silver-loaded lignin microspheres prepared in this invention possess a porous structure. A stable O / W / O type emulsion is formed using composite emulsion technology. After ultrasonic polymerization and cross-linking, the inner and outer oil phases are removed. After drying, the microspheres contain both large pores formed by the inner oil phase and mesh pores formed by water drying in the three-dimensional network. The combination of these two elements creates a porous structure, which helps accelerate mass transfer during microsphere application. Experiments show that if an O / W type primary emulsion is not prepared first and the outer oil phase containing surfactant is added directly for emulsification, the resulting lignin-based microspheres have a poor pore structure; or if the ultrasonic polymerization and cross-linking reaction is insufficient, spherical products cannot be obtained.
[0047] 4. In the lignin porous microspheres loaded with silver nanoparticles prepared by the present invention, the hydroxyl, carboxyl, and amino groups of lignin, as well as the amino groups introduced by the chain extender, have a certain stabilizing effect on the silver nanoparticles, preventing them from agglomerating and increasing, thus solving the problem of easy aggregation of silver nanoparticles.
[0048] 5. The microspheres prepared by this invention have controllable particle size. By using different masses of surfactant and emulsion shear rates, the particle size of lignin porous microspheres can be adjusted from 50 to 500 μm. Larger particle sizes enable the recovery and reuse of lignin microspheres loaded with silver nanoparticles.
[0049] 6. The preparation process provided by this invention is simple, and the oil phase used can be reused through oil-water separation. The raw materials have low cost, high utilization rate, short synthesis time, and a yield of up to 99%. The main component of the microspheres is lignin, which has good biocompatibility, is environmentally friendly, and has virtually no pollution. It can be widely used in wastewater treatment, photocatalytic degradation, and photocatalytic hydrogen production. Attached Figure Description
[0050] Figure 1 This is a scanning electron microscope image of the nano-silver / lignin composite prepared in Example 1.
[0051] Figure 2 This is a scanning electron microscope image of the overall structure of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.
[0052] Figure 3 This is a scanning electron microscope image of the surface of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.
[0053] Figure 4 This is a scanning electron microscope image of the cross-section of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.
[0054] Figure 5 The catalytic performance of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1 on the sodium borohydride reduction reaction of 4-nitrophenol is shown.
[0055] Figure 6 The reaction kinetics curve of sodium borohydride reduction of 4-nitrophenol catalyzed by lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.
[0056] Figure 7 The diagram shows the cyclic catalytic performance of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1. Detailed Implementation
[0057] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.
[0058] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.
[0059] Example 1
[0060] (1) Preparation of nano silver / lignin complex: 3g sodium lignin sulfonate was dissolved in 10g silver ammonia solution (silver content 2wt%), stirred until dissolved, and reacted at 80℃ for 3h to obtain nano silver / lignin complex.
[0061] (2) Preparation of aqueous solution of nano-silver / lignin complex: The pH of nano-silver / lignin complex solution was adjusted to 13.0 with sodium hydroxide; 0.9g epichlorohydrin and 0.1g polyetheramine were added and mixed evenly to obtain nano-silver / lignin aqueous solution;
[0062] (3) Preparation of O / W / O type double emulsion: Add nano silver / lignin aqueous solution to 2.8g of ethyl acetate containing 2wt% Tween-80, and emulsify at 6000rpm for 15min using a homogenizer to obtain W / O type primary emulsion; then add 50.4g of liquid paraffin containing 6wt% Span-60 to W / O primary emulsion, and emulsify at 300rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;
[0063] (4) Preparation of lignin porous microspheres loaded with silver nanoparticles: The O / W / O type double emulsion obtained in step (3) was ultrasonically stirred (power of 240W) for 60 min. After reacting, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured off, and it was washed 3 times with petroleum ether. Then the microspheres were transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were freeze-dried at -40℃ for 48 h to finally obtain lignin porous microspheres loaded with silver nanoparticles.
[0064] Example 2
[0065] (1) Preparation of nano silver / lignin complex: 5g of sulfonated modified alkali lignin was dissolved in 10g of silver ammonia solution (silver content 1wt%), stirred until dissolved, and reacted at 60℃ for 4h to obtain nano silver / lignin complex.
[0066] (2) Preparation of aqueous solution of nano-silver / lignin complex: The pH of nano-silver / lignin complex solution was adjusted to 10.0 with potassium hydroxide; 4.05g formaldehyde solution (mass concentration of 37%) and 0.005g ethylenediamine were added and mixed evenly to obtain nano-silver / lignin aqueous solution;
[0067] (3) Preparation of O / W / O type double emulsion: Add nano silver / lignin aqueous solution to 9.53g of n-heptane containing 0.1wt% polyethylene glycol, and emulsify at 4000rpm for 15min using a homogenizer to obtain W / O type primary emulsion; then add 110g of n-hexane containing 4wt% calcium stearate to W / O primary emulsion, and emulsify at 250rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;
[0068] (4) Preparation of lignin porous microspheres loaded with silver nanoparticles: The O / W / O type double emulsion obtained in step (3) was ultrasonically stirred (power of 150W) for 60 min. After reacting, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured off, and it was washed 6 times with petroleum ether. Then the microspheres were transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were freeze-dried at -10℃ for 48 h to finally obtain lignin porous microspheres loaded with silver nanoparticles.
[0069] Example 3
[0070] (1) Preparation of nano silver / lignin complex: 4g sodium lignin sulfonate was dissolved in 10g silver nitrate solution (silver content 5wt%), stirred until dissolved, and reacted at 80℃ for 2h to obtain nano silver / lignin complex.
[0071] (2) Preparation of aqueous solution of nano-silver / lignin complex: The pH of nano-silver / lignin complex solution was adjusted to 12.0 with sodium hydroxide; 8g of glutaraldehyde solution (mass concentration of 25%) and 0.6g of polyethyleneimine were added and mixed evenly to obtain nano-silver / lignin aqueous solution;
[0072] (3) Preparation of O / W / O type double emulsion: The nano silver / lignin aqueous solution was added to 5.6g of isoamyl alcohol containing 0.5wt% sodium dodecyl sulfate, and emulsified at 6000rpm for 10min using a homogenizer to obtain the W / O type primary emulsion; then 141g of xylene containing 6wt% dodecylphenol polyoxyethylene ether was added to the W / O primary emulsion, and emulsified at 300rpm for 25min using mechanical stirring to obtain the O / W / O type double emulsion;
[0073] (4) Preparation of lignin porous microspheres loaded with silver nanoparticles: The O / W / O type double emulsion obtained in step (3) was ultrasonically stirred (power of 300W) for 60 min. After reacting, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured off, and it was washed 4 times with petroleum ether. Then the microspheres were transferred to a Soxhlet extractor and extracted with ethanol for 12 h. After washing with deionized water, they were freeze-dried at -40℃ for 72 h to finally obtain lignin porous microspheres loaded with silver nanoparticles.
[0074] Example 4
[0075] (1) Preparation of nano-silver / lignin complex: 2g of carboxylated modified solvent-based lignin (extracted from ethanol) was dissolved in 10g of silver nitrate solution (silver content 2wt%), stirred until dissolved, and reacted at 70℃ for 3h to obtain nano-silver / lignin complex.
[0076] (2) Preparation of aqueous solution of nano-silver / lignin complex: The pH of nano-silver / lignin complex solution was adjusted to 11.0 with sodium hydroxide; 0.8g of N,N-methylenebisacrylamide and 0.2g of diethylenetriamine were added and mixed evenly to obtain nano-silver / lignin aqueous solution;
[0077] (3) Preparation of O / W / O type double emulsion: Add nano silver / lignin aqueous solution to 6.5g of isoamyl alcohol containing 1wt% sodium dodecylbenzenesulfonate, and emulsify at 6000rpm for 10min using a homogenizer to obtain W / O type primary emulsion; then add 78g of xylene containing 6wt% glyceryl monostearate to W / O primary emulsion, and emulsify at 200rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;
[0078] (4) Preparation of lignin porous microspheres loaded with silver nanoparticles: The O / W / O type double emulsion obtained in step (3) was ultrasonically stirred (power of 300W) and reacted for 30 min. After standing at normal pressure for 30 min, the upper oil phase was poured off and washed 3 times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were dried at 70°C under vacuum of 76 Pa for 72 h to finally obtain lignin porous microspheres loaded with silver nanoparticles.
[0079] Example 5
[0080] (1) Preparation of nano-silver / lignin complex: 3g of aminated and modified enzymatically hydrolyzed lignin was dissolved in 10g of silver nitrate solution (silver content 2wt%), stirred until dissolved, and reacted at 80℃ for 3h to obtain nano-silver / lignin complex.
[0081] (2) Preparation of aqueous solution of nano-silver / lignin complex: The pH of nano-silver / lignin complex solution was adjusted to 13.0 with sodium hydroxide; 3.75g of glyoxal solution (mass concentration of 40%) and 0.1g of hexamethylenediamine were added and mixed evenly to obtain nano-silver / lignin aqueous solution;
[0082] (3) Preparation of O / W / O type double emulsion: The nano silver / lignin aqueous solution was added to 5.6g of ethyl acetate containing 0.6wt% sodium dodecyl sulfate, and emulsified at 5000rpm for 15min using a homogenizer to obtain the W / O type primary emulsion; then 90g of n-hexane containing 6wt% Span-60 was added to the W / O primary emulsion, and emulsified at 250rpm for 30min using mechanical stirring to obtain the O / W / O type double emulsion;
[0083] (4) Preparation of lignin porous microspheres loaded with silver nanoparticles: The O / W / O type double emulsion obtained in step (3) was ultrasonically stirred (power of 250W) for 30 min, and then allowed to stand at normal pressure for 20 min. The upper oil phase was poured off and washed three times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, the microspheres were freeze-dried at -10℃ for 48 h to finally obtain lignin porous microspheres loaded with silver nanoparticles.
[0084] Example 6
[0085] (1) Preparation of nano silver / lignin complex: 2.5g sodium lignin sulfonate was dissolved in 10g silver ammonia solution (silver content 2wt%), stirred until dissolved, and reacted at 70℃ for 3h to obtain nano silver / lignin complex.
[0086] (2) Preparation of aqueous solution of nano-silver / lignin complex: The pH of nano-silver / lignin complex solution was adjusted to 13.0 with sodium hydroxide; 4g of glutaraldehyde solution (mass concentration of 25%) and 0.15g of triethylenetetramine were added and mixed evenly to obtain nano-silver / lignin aqueous solution;
[0087] (3) Preparation of O / W / O type double emulsion: Add nano silver / lignin aqueous solution to 5.55g of n-heptane containing 0.1wt% polyethylene glycol, and emulsify at 6000rpm for 15min using a homogenizer to obtain W / O type primary emulsion; then add 88g of n-hexane containing 2wt% calcium stearate to W / O primary emulsion, and emulsify at 250rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion;
[0088] (4) Preparation of lignin porous microspheres loaded with silver nanoparticles: The O / W / O type double emulsion obtained in step (3) was ultrasonically stirred (power of 250W) for 45 min. After reacting, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured off, and it was washed 6 times with petroleum ether. Then the microspheres were transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were freeze-dried at -40℃ for 48 h to finally obtain lignin porous microspheres loaded with silver nanoparticles.
[0089] Example 7
[0090] (1) Preparation of nano silver / lignin complex: 3g sodium lignin sulfonate was dissolved in 10g silver ammonia solution (silver content 3wt%), stirred until dissolved, and reacted at 80℃ for 2h to obtain nano silver / lignin complex.
[0091] (2) Preparation of aqueous solution of nano-silver / lignin complex: The pH of nano-silver / lignin complex solution was adjusted to 13.0 with sodium hydroxide; 1.5g N,N-methylenebisacrylamide and 0.45g triethylenetetramine were added and mixed evenly to obtain nano-silver / lignin aqueous solution;
[0092] (3) Preparation of O / W / O type double emulsion: Add nano silver / lignin aqueous solution to 5g of isoamyl alcohol containing 0.8wt% sucrose ester, and emulsify at 6000rpm for 15min using a homogenizer to obtain W / O type primary emulsion; then add 80g of cyclohexane containing 3wt% dodecylphenol polyoxyethylene ether to W / O primary emulsion, and emulsify at 250rpm for 30min using mechanical stirring to obtain O / W / O type double emulsion;
[0093] (4) Preparation of lignin porous microspheres loaded with silver nanoparticles: The O / W / O type double emulsion obtained in step (3) was ultrasonically stirred (power of 200W) for 60 min, and then allowed to stand at normal pressure for 20 min. The upper oil phase was poured off and washed three times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 24 h. After washing with deionized water, they were dried at 30°C under a vacuum of 90 Pa for 48 h to finally obtain lignin porous microspheres loaded with silver nanoparticles.
[0094] Example effect description:
[0095] The effect is illustrated using Example 1 as an example.
[0096] Figure 1 The image shows the SEM image of the nano-silver / lignin composite prepared in step (1) of this embodiment. As can be seen from the image, the nano-silver / lignin composite has a small particle size and uniform distribution. Figure 2 The image shows the SEM image of the nano-silver / lignin porous microspheres prepared in Example 1. It can be seen that the product is a regular sphere with a particle size of about 400 μm and abundant pores on the surface. Figure 3 The image shows the surface mapping of the nano-silver / lignin porous microspheres prepared in Example 1. As can be seen from the image, the nano-silver was successfully loaded onto the lignin porous microspheres and is uniformly distributed on the surface of the microspheres. Figure 4 This is a cross-sectional SEM image of the nano-silver / lignin porous microspheres prepared in Example 1. The image shows pores on the surface of the microspheres and a rich network of interconnected pores inside. The lignin, after ultrasonic polymerization and cross-linking, forms microspheres with a certain mechanical strength. Furthermore, the rapid sublimation of the aqueous phase within the microspheres during drying results in a large number of pores inside the microspheres.
[0097] To investigate the catalytic performance of the nano-silver / lignin porous microspheres prepared in Example 1, the reduction of p-nitrophenol (4-NP) with NaBH4 was selected as a model reaction. The specific procedure was as follows: 200 μL of 0.01 mol / L 4-NP solution was added to 20 mL of 0.03 mol / L NaBH4 solution, followed by 20 mg of the microsphere sample. The UV-Vis spectrum of the microsphere sample catalyzing the reduction of p-nitrophenol at 25°C was measured online using a UV-Vis spectrophotometer as a function of reaction time. Figure 5The UV absorption spectrum of the reduction of 4-NP catalyzed by nano-silver / lignin porous microspheres shows that as the reaction proceeds, the intensity of the characteristic absorption peak of 4-NP at 400 nm gradually decreases, while the characteristic absorption peak of p-aminophenol (4-AP) at 300 nm gradually increases. After 10 min of catalytic reduction, the absorption peak of 4-NP at 400 nm disappears, and the solution changes from yellow to colorless, indicating that all 4-NP is converted to 4-AP. This result demonstrates that the nano-silver / lignin porous microspheres prepared in Example 1 have good catalytic activity for the reduction of p-nitrophenol. Figure 6 The kinetic diagram of the 4-NP reduction catalyzed by nano-silver / lignin porous microspheres shows that the catalytic reaction follows pseudo-first-order kinetics, with a rate constant of 0.234 min⁻¹. -1 Furthermore, the nano-silver / lignin porous microspheres prepared in Examples 2, 3, 4, and 5 were applied to the NaBH4 reduction of 4-NP reaction under the same conditions as in Example 1. The times required for the complete reduction of 4-NP by NaBH4 catalyzed by the above five types of nano-silver / lignin porous microspheres were measured to be 10 min, 12 min, 12 min, and 10 min, respectively. This indicates that the nano-silver / lignin porous microspheres prepared in this invention have good catalytic ability.
[0098] The catalytic performance of the nano-silver / lignin porous microspheres prepared in Example 1 after multiple recycling was tested. Specifically, after each catalytic reaction, the microsphere catalyst was separated from the reaction solution by filtration, washed three times each with ethanol and deionized water, and then dried for later use. 200 μL of 0.01 mol / L 4-NP solution was added to 20 mL of 0.03 mol / L NaBH4 solution, followed by 20 mg of the microsphere sample. The UV-Vis spectrum of the microsphere sample catalyzing the reduction of p-nitrophenol was measured online at 25°C for 15 min using a UV-Vis spectrophotometer, showing the change in UV-Vis spectrum with reaction time. Figure 7 It was observed that the absorption peak of 4-NP disappeared at 400 nm, while the characteristic absorption peak of 4-AP increased at 300 nm, and the solution changed from yellow to colorless, indicating that all 4-NP was converted to 4-AP. After four cycles, the nano-silver / lignin porous microspheres still maintained high catalytic activity. Simultaneously, the catalytic performance of the nano-silver / lignin porous microspheres prepared in Examples 2, 3, 4, and 5 after multiple recycling and reuse following the experimental steps of Example 1 was tested. The results showed that all four types of nano-silver / lignin porous microspheres could be repeatedly catalyzed at least four times, and maintained excellent catalytic performance in the fourth catalytic reaction, converting 98% of 4-NP to 4-AP within 15 minutes. This demonstrates that the nano-silver / lignin porous microspheres prepared in this invention have good recyclability.
[0099] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.
Claims
1. A method for preparing lignin porous microspheres loaded with silver nanoparticles, characterized in that, Includes the following steps: (1) Add lignin to a silver-containing solution, dissolve it, and then heat it to react, thus obtaining a nano-silver / lignin complex solution; (2) Adjust the nano-silver / lignin complex solution to alkaline and mix it evenly with crosslinking agent and chain extender to obtain nano-silver / lignin aqueous solution; (3) Mix the nano-silver / lignin aqueous solution with the inner oil phase containing surfactant and emulsify to obtain an O / W type primary emulsion; then mix the O / W type primary emulsion with the outer oil phase containing surfactant and emulsify to obtain an O / W / O type secondary emulsion; (4) After ultrasonic reaction of O / W / O type double emulsion, after the reaction is completed, remove the oil phase, wash, and dry to obtain lignin porous microspheres loaded with silver nanoparticles; The crosslinking agent in step (2) is at least one of formaldehyde, glutaraldehyde, glyoxal, epichlorohydrin, and N,N-methylenebisacrylamide; the amount of crosslinking agent used is 30-50% of the lignin content; The chain extender in step (2) is at least one selected from ethylenediamine, hexamethylenediamine, polyetheramine, polyethyleneimine, triethylenetetramine, and diethylenetriamine; the amount of the chain extender is 0.1% to 15% of the lignin content; In step (3), the surfactant in the inner oil phase containing the surfactant is at least one of Tween-80, sucrose ester, polyethylene glycol, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate; the oil phase is at least one of toluene, isoamyl alcohol, n-heptane, and ethyl acetate. In step (3), the surfactant in the outer oil phase containing surfactant is at least one of Span-60, glyceryl monostearate, calcium stearate and dodecylphenol polyoxyethylene ether; the oil phase is at least one of cyclohexane, xylene, n-hexane and liquid paraffin.
2. The method for preparing lignin porous microspheres loaded with silver nanoparticles according to claim 1, characterized in that, The ultrasonic power of the ultrasonic reaction in step (4) is 150-300 W; the reaction time is 30-60 min.
3. The method for preparing lignin porous microspheres loaded with silver nanoparticles according to claim 1, characterized in that, The mass ratio of the lignin aqueous solution and the inner oil phase containing the surfactant in step (3) is 2:1 to 5:1; the mass ratio of the O / W type primary emulsion and the outer oil phase containing the surfactant in step (3) is 1:3 to 1:
5.
4. The method for preparing lignin porous microspheres loaded with silver nanoparticles according to claim 1, characterized in that, The inner oil phase containing surfactant in step (3) consists of surfactant and oil phase, wherein the surfactant accounts for 0.1 to 2% of the total mass of the inner oil phase; the outer oil phase containing surfactant in step (3) consists of surfactant and oil phase, wherein the surfactant accounts for 2 to 6% of the total mass of the outer oil phase.
5. The method for preparing lignin porous microspheres loaded with silver nanoparticles according to claim 1, characterized in that, The lignin in step (1) is at least one of sodium lignin sulfonate, sulfonated alkali lignin, carboxylated alkali lignin, aminated alkali lignin, sulfonated solvent-type lignin, carboxylated solvent-type lignin, aminated solvent-type lignin, sulfonated enzymatically hydrolyzed lignin, carboxylated enzymatically hydrolyzed lignin, and aminated enzymatically hydrolyzed lignin. The silver-containing solution in step (1) is at least one of silver nitrate solution or silver ammonia solution; the silver content in the silver-containing solution is 1-5 wt%. The mass ratio of lignin to silver-containing solution in step (1) is 1:2 to 1:5; The heating reaction in step (1) is carried out at a temperature of 60–80 °C; The heating reaction in step (1) takes 2 to 4 hours; The alkalinity mentioned in step (2) refers to a pH of 10 to 13; The alkali used in step (2) to adjust the nano-silver / lignin complex solution to alkalinity is at least one of sodium hydroxide and potassium hydroxide.
6. The method for preparing lignin porous microspheres loaded with silver nanoparticles according to claim 1, characterized in that, The emulsification conditions for the O / W type colostrum in step (3) are: shearing at 3000-6000 rpm for 10-15 min; the emulsification conditions for the O / W / O type double emulsion are: shearing at 200-300 rpm for 25-40 min. The method for removing the oil phase in step (4) is as follows: let it stand at normal pressure for 10 to 30 minutes, and then pour out the upper oil phase; The washing process in step (4) is as follows: first wash with petroleum ether 3 to 6 times, then transfer the microspheres to a Soxhlet extractor and extract with ethanol for 12 to 24 hours; The drying in step (4) is: freeze drying at -40 to -10°C for 48 to 72 h or drying at 30 to 70°C under a vacuum of 76 to 90 Pa for 48 to 72 h.
7. A lignin porous microsphere loaded with silver nanoparticles is prepared by the preparation method according to any one of claims 1 to 6.
8. The application of the lignin porous microspheres loaded with silver nanoparticles as a catalyst in oxidation, reduction, and CC coupling reactions as described in claim 7.