Lignin porous microspheres loaded with metal nanoparticles, and preparation method and application thereof

Abstract

The application discloses a kind of lignin porous microspheres loaded with metal nanoparticles and its preparation method and application.The alkali lignin solution is mixed with crosslinking agent, chain extender homogeneous aqueous solution as water phase, mixed with internal oil phase containing surfactant, emulsified, and O / W primary emulsion is formed;Then the primary emulsion is mixed with external oil phase containing surfactant, emulsified, and O / W / O type complex emulsion is obtained;Then the crosslinking reaction is completed under ultrasonic, and after the reaction is finished, the oil phase is removed, and after washing, lignin porous microspheres are formed;Finally, the lignin porous microspheres are suspended and dispersed in the aqueous solution containing metal ions, and after heating or ultrasonic reaction, the lignin porous microspheres loaded with metal nanoparticles are obtained by separation and drying.The application has good balling effect, controllable particle size, rich surface and internal pore;The microspheres have good biocompatibility, biodegradability, better catalytic performance, and are suitable for bed layer catalysis, and have great application potential.

Description

Technical Field

[0001] This invention belongs to the field of porous microsphere preparation technology, specifically relating to a lignin porous microsphere loaded with metal nanoparticles, its preparation method and application. Background Technology

[0002] Metal nanoparticles possess many unique physical and chemical properties, showing promising prospects in sensor, optics, and catalyst fields. However, their poor stability and tendency to aggregate during reactions limit their application. To address this issue, researchers have proposed the preparation of supported catalysts. By loading metal nanoparticles onto a support, these nanoparticles can exhibit good stability, catalytic activity, and recyclability. Commonly used supports include metal oxides, dendritic polymers, polymer microspheres, silica, and biomass. Among these, biomass is favored by researchers due to its renewable nature, abundant resources, and numerous functional groups.

[0003] Lignin is the second largest biomass resource in nature, a natural high-molecular polymer with a three-dimensional network structure. In the paper industry alone, a large amount of lignin is produced annually as a byproduct. Lignin molecules contain abundant active groups such as hydroxyl, carboxyl, and sulfonic acid groups. Among these active groups, the hydroxyl group has a reducing effect on metal ions, avoiding the use of large amounts of toxic chemical reagents in the preparation of metal nanoparticles. Currently, researchers mostly choose lignin sulfonates or dissolved alkali lignin to prepare metal nanoparticles, which allows for efficient reduction. For example, Adina Arvinte et al. used lignin sulfonates as a reducing agent and silver nitrate as a silver source, coating the resulting product onto an electrode for the electrocatalytic oxidation of p-nitrophenol. Their results showed that the product exhibited good electrocatalytic activity. Jian Yang et al. successfully prepared NaLS@AgNPs nanocomposite materials by freeze-drying sodium lignosulfonate and silver nitrate at 60℃. Experimental results showed that it exhibited excellent catalytic performance in the degradation of methylene blue (MB) (reaction time was only 150 s, removal rate was close to 100%, k = 20.4 × 10⁻⁶). -3 s -1Our research group modified alkali lignin by amination, which appropriately improved its solubility and increased the content of effective functional groups participating in the silver reduction reaction. We successfully prepared an amination lignin / silver nanocomposite and applied it to a 4-NP catalytic reaction. The results showed that the composite possessed high catalytic performance and good recycling performance. From the above examples, we can see that lignin can act as a reducing agent, dispersant, and stabilizer in the preparation of metal nanoparticles, greatly reducing the use of chemical reagents in this process. However, the metal nanoparticle / lignin composite materials prepared in the above examples are in powder form, making them difficult to recycle and limiting their application.

[0004] Lignin porous microspheres possess a large specific surface area, enabling them to fully contact and adsorb substrates; their good hydrodynamic properties make them suitable for bed adsorption; and their strong mechanical properties give them excellent recovery performance. Therefore, loading metal nanoparticles onto lignin porous microspheres shows great promise, and there is an urgent need to develop a method for preparing lignin-based porous microspheres loaded with metal nanoparticles. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing lignin porous microspheres loaded with metal nanoparticles.

[0006] The principle of this invention for preparing lignin porous microspheres loaded with metal nanoparticles is as follows: first, lignin porous microspheres are prepared, and then the metal nanoparticles are reduced in situ. First, lignin porous microspheres are prepared based on ultrasonic polymerization of an O / W / O type composite emulsion. An aqueous solution of lignin is used as the aqueous phase to prepare the O / W / O type composite emulsion. Under ultrasonic action, lignin and chain extenders are linked together by a crosslinking agent. The chain extender lengthens the lignin molecular backbone, and the crosslinking agent forms a network structure of the lignin molecular chains, resulting in lignin microspheres with high flexibility and high crosslinking rigidity. This allows for drying and pore formation without sphere collapse. 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 inner oil phase together construct the porous structure of the lignin microspheres. Then, the lignin porous microspheres are suspended and dispersed in an aqueous solution of a metal salt. After heating or ultrasonic reaction, the hydroxyl groups on the lignin porous microspheres can reduce the metal ions to metal nanoparticles. Separation and drying yield the lignin porous microspheres loaded with metal nanoparticles.

[0007] Another object of the present invention is to provide lignin porous microspheres loaded with metal 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 metal nanoparticles.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for preparing lignin porous microspheres loaded with metal nanoparticles includes the following steps:

[0011] (1) Mix the lignin alkaline solution, crosslinking agent and chain extender evenly to obtain a lignin aqueous solution;

[0012] (2) Mix the lignin aqueous solution and the inner oil phase containing surfactant, emulsify, and obtain O / W type primary emulsion; then mix the O / W type primary emulsion and the outer oil phase containing surfactant, emulsify, and obtain O / W / O type secondary emulsion;

[0013] (3) The O / W / O type double emulsion was subjected to ultrasonic reaction. After the reaction was completed, the oil phase was removed and the mixture was washed to obtain lignin porous microspheres.

[0014] (4) The lignin porous microspheres are suspended and dispersed in an aqueous solution of metal salt, and after heating or ultrasonic reaction, they are separated and dried to obtain lignin porous microspheres loaded with metal nanoparticles.

[0015] Preferably, in the lignin alkaline solution of step (1), the lignin is at least one of alkali lignin, solvent-based lignin, enzymatically hydrolyzed lignin, sodium lignin sulfonate, and amination-modified products of these lignins; more preferably, it is at least one of sodium lignin sulfonate, amination-modified sodium lignin sulfonate, alkali lignin, and enzymatically hydrolyzed lignin.

[0016] Preferably, the lignin alkaline solution in step (1) is obtained by adding lignin to an alkaline solution, wherein the alkaline solution is at least one of sodium hydroxide solution and potassium hydroxide solution, and the concentration of the alkaline solution is 0.5 to 2.0 mol / L; the mass fraction of lignin in the lignin alkaline solution is 40 to 65%.

[0017] Preferably, the crosslinking agent in step (1) 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.

[0018] Preferably, the chain extender in step (1) is at least one of ethylenediamine, hexamethylenediamine, polyetheramine, polyethyleneimine, triethylenetetramine, and diethylenetriamine; the amount of the chain extender is 0.1-15% of the lignin content.

[0019] Preferably, the inner oil phase containing surfactant in step (2) consists of surfactant and oil phase, wherein the surfactant accounts for 0.1 to 2% of the total mass of the inner oil phase.

[0020] Preferably, in the inner oil phase containing surfactant in step (2), 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.

[0021] Preferably, the mass ratio of the lignin aqueous solution and the internal oil phase containing the surfactant in step (2) is 3:1 to 6:1.

[0022] Preferably, the external oil phase containing surfactant in step (2) is composed of surfactant and oil phase, wherein the surfactant accounts for 2 to 6% of the total mass of the external oil phase.

[0023] Preferably, in the external oil phase containing surfactant in step (2), 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.

[0024] Preferably, the mass ratio of the O / W type primary emulsion and the external oil phase containing the surfactant in step (2) is 1:3 to 1:5.

[0025] Preferably, the emulsification conditions for the O / W type primary emulsion in step (2) are: shearing at 3000-6000 rpm for 10-15 min; and the emulsification conditions for the O / W / O type secondary emulsion are: shearing at 200-300 rpm for 25-40 min.

[0026] Preferably, the ultrasonic power of the ultrasonic reaction in step (3) is 150-300W; the reaction time is 30-60min.

[0027] Preferably, the method for removing the oil phase in step (3) is as follows: let it stand at normal pressure for 10 to 30 minutes, and then pour out the upper oil phase.

[0028] Preferably, the washing in step (3) 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.

[0029] Preferably, in the aqueous solution of the metal salt in step (4), the metal salt is at least one of AgNO3, HAuCl4, H2PtCl6 and PdCl2.

[0030] Preferably, in the aqueous solution of the metal salt in step (4), the concentration of the metal salt is 10 to 100 mmol / L.

[0031] Preferably, the mass ratio of the lignin porous microspheres to the metal salt in step (4) is 1:2 to 1:17.

[0032] Preferably, the heating reaction in step (4) is carried out at a temperature of 25–80°C for a time of 0.5–12 h.

[0033] Preferably, the ultrasonic power of the ultrasonic reaction in step (4) is 150-300W, the temperature is 30-50℃, and the time is 0.5-2h.

[0034] Preferably, the separation in step (4) involves filtering the microspheres and washing them 2-3 times with deionized water; the drying involves drying them at a vacuum of 76-90 Pa and a temperature of 50-70 °C for 48-72 hours.

[0035] A lignin porous microsphere loaded with metal nanoparticles was prepared by the above method.

[0036] The lignin porous microspheres loaded with metal nanoparticles prepared in this invention have a particle size of 50–500 μm.

[0037] The above-mentioned application of lignin porous microspheres loaded with metal nanoparticles in the field of catalysis.

[0038] Preferably, the catalytic field is the catalytic hydrogenation of organic compounds.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] 1. This invention uses ultrasound-assisted polymerization to prepare lignin microspheres. Under the action of ultrasound, lignin undergoes a certain degree of polymerization, which increases the molecular weight of lignin and improves the cross-linking strength of the microspheres. At the same time, the cross-linking agent connects lignin with the chain extender, giving the microspheres a certain degree of flexibility, which is beneficial for the formation of pores after drying.

[0041] 2. The microspheres prepared by this invention have 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 internal oil phase and mesh pores formed by water drying in the three-dimensional network. The combination of these two elements forms a rich porous structure.

[0042] 3. The porous structure of the microspheres prepared in this invention ensures sufficient contact with the reaction substrate during catalysis, providing more reaction sites and thus accelerating the reaction rate. Their excellent hydrodynamic and mechanical properties make them suitable for bed catalysis. The excellent adsorption properties of lignin for various hydrophilic and hydrophobic substances can enrich the reaction substrate, further promoting the catalytic reaction of the substrate on the nano-metal particles.

[0043] 4. The high specific surface area and abundant reducing groups of the lignin porous microspheres prepared by this invention can achieve full reduction and loading of metal ions. Furthermore, the amino groups help to bind the reduced metal elements through coordination bonds, resulting in small particle size, narrow distribution, uniform distribution and firm binding of the reduced metal nanoparticles on the microspheres, making them less likely to fall off during use.

[0044] 5. The microspheres prepared by this invention have controllable particle size. By using different masses of surfactants and emulsion shear rates, the particle size of lignin porous microspheres can be adjusted from 50 to 500 μm. Attached Figure Description

[0045] Figure 1 This is a scanning electron microscope image of the overall structure of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.

[0046] Figure 2 This is a scanning electron microscope image of the surface of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.

[0047] Figure 3 This is a scanning electron microscope image of the cross-section of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.

[0048] Figure 4 The image shows the SEM-EDS characterization of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.

[0049] Figure 5 This is a TEM image of silver nanoparticles on lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.

[0050] Figure 6 The graph shows the catalytic reduction performance of p-nitrophenol by the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1.

[0051] Figure 7 The graph shows the cyclic performance of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1 for the catalytic reduction of p-nitrophenol.

[0052] Figure 8 The catalytic reduction performance of p-nitrophenol by the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1. Detailed Implementation

[0053] 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.

[0054] 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.

[0055] Example 1

[0056] (1) Preparation of lignin aqueous solution: Dissolve 18g of sodium lignin sulfonate in 1.0mol / L sodium hydroxide solution to prepare 30g of 60wt% lignin base solution; add 7.2g of epichlorohydrin and 2.7g of polyetheramine, mix well to obtain lignin aqueous solution.

[0057] (2) Preparation of O / W / O type double emulsion: 8g of lignin aqueous solution was added to ethyl acetate containing 2wt% Tween-80 and emulsified at 6000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 144g of liquid paraffin containing 6wt% Span-60 was added to O / W primary emulsion and emulsified at 300rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion.

[0058] (3) Preparation of lignin porous microspheres: The O / W / O type double emulsion obtained in step (2) was stirred by ultrasonication (power of 240W) for 60 min. After reaction, it was allowed to stand at normal pressure for 10 min. The upper oil phase was poured out 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, lignin porous microspheres were obtained.

[0059] (4) Preparation of lignin porous microspheres loaded with metal nanoparticles: 0.2 g of lignin porous microspheres obtained in step (3) were suspended and dispersed in 100 mL of AgNO3 aqueous solution (concentration of 50 mmol / L). After ultrasonic reaction (power of 300 W, temperature of 30 °C) for 2 h, the microspheres were filtered and washed with deionized water 2 to 3 times. Finally, they were dried at 50 °C under vacuum of 76 Pa for 48 h to obtain lignin porous microspheres loaded with silver nanoparticles.

[0060] Example 2

[0061] (1) Preparation of lignin aqueous solution: 12g of alkali lignin was dissolved in 2.0mol / L sodium hydroxide solution to prepare 30g of 40wt% lignin alkali solution; 9.73g of formaldehyde solution (mass concentration of 37%) and 1.8g of ethylenediamine were added and mixed evenly to obtain lignin aqueous solution.

[0062] (2) Preparation of O / W / O type double emulsion: The lignin aqueous solution was added to 7.5g of n-heptane containing 0.1wt% polyethylene glycol and emulsified at 4000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then 155g of n-hexane containing 4wt% calcium stearate was added to the O / W primary emulsion and emulsified at 250rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion.

[0063] (3) Preparation of lignin porous microspheres: The O / W / O type double emulsion obtained in step (2) was stirred by ultrasonication (power of 150W) for 60 min. After reaction, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured out, 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, lignin porous microspheres were obtained.

[0064] (4) Preparation of lignin porous microspheres loaded with metal nanoparticles: 0.2 g of lignin porous microspheres obtained in step (3) were suspended and dispersed in 100 mL of HAuCl4 aqueous solution (concentration of 100 mmol / L). After ultrasonic reaction (power of 150 W, temperature of 50 °C) for 0.5 h, the microspheres were filtered and washed with deionized water 2 to 3 times. Finally, they were dried at 50 °C under vacuum of 90 Pa for 72 h to obtain lignin porous microspheres loaded with gold nanoparticles.

[0065] Example 3

[0066] (1) Preparation of lignin aqueous solution: Dissolve 15g sodium lignin sulfonate in 1.5mol / L potassium hydroxide solution to prepare 30g 50wt% lignin base solution; add 18g glutaraldehyde solution (mass concentration of 25%) and 1.5g triethylenetetramine, mix well to obtain lignin aqueous solution.

[0067] (2) Preparation of O / W / O type double emulsion: Add 10g of lignin aqueous solution to 10g of toluene containing 0.5wt% sodium dodecylbenzenesulfonate, and emulsify at 4000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then add 180g of cyclohexane containing 6wt% dodecylphenol polyoxyethylene ether to O / W primary emulsion, and emulsify at 250rpm for 30min using mechanical stirring to obtain O / W / O type double emulsion.

[0068] (3) Preparation of lignin porous microspheres: The O / W / O type double emulsion obtained in step (2) was stirred by ultrasonication (power of 300W) for 60 min. After reaction, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured out, and it was washed 3 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, lignin porous microspheres were obtained.

[0069] (4) Preparation of lignin porous microspheres loaded with metal nanoparticles: 0.2 g of lignin porous microspheres obtained in step (3) were suspended and dispersed in 100 mL of H2PtCl6 aqueous solution (concentration of 10 mmol / L). After heating and reacting at 80 °C for 2 h, the microspheres were filtered and washed 2 to 3 times with deionized water. Finally, they were dried at 60 °C under a vacuum of 90 Pa to obtain lignin porous microspheres loaded with platinum nanoparticles.

[0070] Example 4

[0071] (1) Preparation of lignin aqueous solution: 19.5g sodium lignin sulfonate was dissolved in 0.5mol / L potassium hydroxide solution to prepare 30g 65wt% lignin alkali solution; 7.8g N,N-methylenebisacrylamide and 0.975g diethylenetriamine were added and mixed evenly to obtain lignin aqueous solution.

[0072] (2) Preparation of O / W / O type double emulsion: Add 8g of lignin aqueous solution to isoamyl alcohol containing 0.5wt% sodium dodecylbenzenesulfonate, and emulsify at 6000rpm for 10min using a homogenizer to obtain O / W type primary emulsion; then add 170g of xylene containing 2wt% glyceryl monostearate to O / W primary emulsion, and emulsify at 250rpm for 40min using mechanical stirring to obtain O / W / O type double emulsion.

[0073] (3) Preparation of lignin porous microspheres: The O / W / O type double emulsion obtained in step (2) was stirred by ultrasonication (power of 200W) for 60 min. After reaction, it was allowed to stand at normal pressure for 10 min, the upper oil phase was poured out, 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, lignin porous microspheres were obtained.

[0074] (4) Preparation of lignin porous microspheres loaded with metal nanoparticles: 0.2 g of lignin porous microspheres obtained in step (3) were suspended and dispersed in 100 mL of PdCl2 aqueous solution (concentration of 70 mmol / L). After reacting at 25 °C for 12 h, the microspheres were filtered and washed with deionized water 2 to 3 times. Finally, they were dried at 50 °C under a vacuum of 76 Pa to obtain lignin porous microspheres loaded with palladium nanoparticles.

[0075] Example 5

[0076] (1) Preparation of lignin aqueous solution: 12g of solvent-based lignin (extracted from ethanol) was dissolved in a 1.0mol / L mixed solution of sodium hydroxide and potassium hydroxide to prepare a 30g 40wt% lignin alkaline solution; 9g of glyoxal solution (concentration of 40%) and 0.3g of hexamethylenediamine were added and mixed evenly to obtain the lignin aqueous solution.

[0077] (2) Preparation of O / W / O type double emulsion: 7.86 g of lignin aqueous solution was added to toluene containing 0.3 wt% sodium dodecyl sulfate and emulsified at 4000 rpm for 15 min using a homogenizer to obtain O / W type primary emulsion; then 188 g of n-hexane containing 6 wt% calcium stearate was added to O / W primary emulsion and emulsified at 250 rpm for 30 min using mechanical stirring to obtain O / W / O type double emulsion.

[0078] (3) Preparation of lignin porous microspheres: The O / W / O type double emulsion obtained in step (2) was stirred by ultrasonication (power of 150W) for 30 min. After reaction, it was allowed to stand at normal pressure for 10 min. The upper oil phase was poured out 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, lignin porous microspheres were obtained.

[0079] (4) Preparation of lignin porous microspheres loaded with metal nanoparticles: 0.2 g of lignin porous microspheres obtained in step (3) were suspended and dispersed in 100 mL of HAuCl4 aqueous solution (concentration of 50 mmol / L). After heating and reacting at 80 °C for 0.5 h, the microspheres were filtered and washed with deionized water 2 to 3 times. Finally, they were dried at 70 °C under a vacuum of 90 Pa for 48 h to obtain lignin porous microspheres loaded with gold nanoparticles.

[0080] Example 6

[0081] (1) Preparation of lignin aqueous solution: 12g of amination-modified sodium lignin sulfonate (specific preparation method: dissolve 30g of sodium lignin sulfonate in 180g of deionized water, add 3g of formaldehyde solution (mass concentration is 37%), 6g of hexamethylenediamine and 5g of sodium hydroxide, stir thoroughly, react at 70℃ for 4h, after the reaction is completed, add 3mol / L hydrochloric acid dropwise while stirring to allow the amination-modified sodium lignin sulfonate to fully precipitate, wash, filter and dry to obtain the product) was dissolved in 1.5mol / L sodium hydroxide solution to prepare 30g of 40wt% lignin alkali solution; add 14.4g of glutaraldehyde solution (mass concentration is 25%) and 0.75g of polyethyleneimine, mix well to obtain lignin aqueous solution.

[0082] (2) Preparation of O / W / O type double emulsion: Add lignin aqueous solution to 10g of n-heptane containing 2wt% Tween-80, and emulsify at 3000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then add 180g of n-hexane containing 2wt% Span-60 to O / W primary emulsion, and emulsify at 200rpm for 30min using mechanical stirring to obtain O / W / O type double emulsion.

[0083] (3) Preparation of lignin porous microspheres: The O / W / O type double emulsion obtained in step (2) was ultrasonically stirred (power of 200W) for 50 min, and then allowed to stand at normal pressure for 10 min. The upper oil phase was poured out and washed 6 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, lignin porous microspheres were obtained.

[0084] (4) Preparation of lignin porous microspheres loaded with metal nanoparticles: 0.2 g of lignin porous microspheres obtained in step (3) were suspended and dispersed in 100 mL of H2PtCl6 aqueous solution (concentration of 40 mmol / L). After ultrasonic reaction (power of 240 W, temperature of 30 °C) for 1 h, the microspheres were filtered and washed with deionized water 2 to 3 times. Finally, they were dried at 50 °C under vacuum of 90 Pa for 48 h to obtain lignin porous microspheres loaded with platinum nanoparticles.

[0085] Example 7

[0086] (1) Preparation of lignin aqueous solution: 12g of enzymatically hydrolyzed lignin was dissolved in 1.5mol / L potassium hydroxide solution to prepare 30g of 40wt% lignin alkaline solution; 6g of N,N-methylenebisacrylamide and 0.012g of diethylenetriamine were added and mixed evenly to obtain lignin aqueous solution.

[0087] (2) Preparation of O / W / O type double emulsion: Add lignin aqueous solution to 8g of isoamyl alcohol containing 0.5wt% sucrose ester, and emulsify at 5000rpm for 15min using a homogenizer to obtain O / W type primary emulsion; then add 220g of cyclohexane containing 3wt% dodecylphenol polyoxyethylene ether to O / W primary emulsion, and emulsify at 300rpm for 25min using mechanical stirring to obtain O / W / O type double emulsion.

[0088] (3) Preparation of lignin porous microspheres: The O / W / O type double emulsion obtained in step (2) was stirred by ultrasonication (power of 300W) for 60 min. After reaction, it was allowed to stand at normal pressure for 30 min. The upper oil phase was poured out and washed 3 times with petroleum ether. The microspheres were then transferred to a Soxhlet extractor and extracted with ethanol for 12 h. After washing with deionized water, lignin porous microspheres were obtained.

[0089] (4) Preparation of lignin porous microspheres loaded with metal nanoparticles: 0.2 g of lignin porous microspheres obtained in step (3) were suspended and dispersed in 100 mL of AgNO3 aqueous solution (concentration of 50 mmol / L). After heating and reacting at 60 °C for 2 h, the microspheres were filtered and washed with deionized water 2 to 3 times. Finally, they were dried at 50 °C under a vacuum of 76 Pa for 48 h to obtain lignin porous microspheres loaded with silver nanoparticles.

[0090] Example effect description:

[0091] The effect is illustrated using Example 1 as an example.

[0092] Figure 1 and Figure 2 This is an SEM image of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1. The microspheres are regular spherical in shape, with abundant small pores on their surface, and it can be seen that there are many silver nanoparticles on the surface of the microspheres. Figure 3 This is a cross-sectional SEM image of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1. As can be seen from the image, the microspheres have a porous structure with abundant interconnected pores inside. After ultrasonic polymerization and cross-linking, lignin forms microspheres with a certain mechanical strength. During the removal and drying process of the oil and water phases inside the microspheres, a large number of pores are generated inside the microspheres.

[0093] Figure 4 This is a SEM-EDS characterization of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1. As shown in the figure, the Ag content is 1.14%, and it is relatively uniformly distributed on the surface of the microspheres.

[0094] Figure 5 This is a TEM image of the silver nanoparticles on the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1. As can be seen from the image, the particle size of the silver nanoparticles on the microspheres is between 10 and 30 nm.

[0095] To investigate the catalytic performance of the silver / lignin porous microspheres prepared in Example 1, the reduction of p-nitrophenol (4-NP) with NaBH4 was used as a model reaction. The specific procedure was as follows: 200 μL of a 0.01 mol / L p-nitrophenol solution was transferred to a 50 mL beaker, and 20 mL of freshly prepared 0.03 mol / L sodium borohydride solution was added. After mixing thoroughly, 20 mg of the silver-loaded lignin porous microsphere sample was added. Samples were taken at regular intervals. 1 mL of the reaction solution was filtered through a 0.22 μm filter using a syringe, and the reaction was detected using a UV spectrophotometer (25 °C). The UV-Vis spectrum of the reaction solution in the wavelength range of 250-500 nm over time was recorded. Figure 6 As the reaction proceeds, the characteristic absorption peak of p-nitrophenol at 400 nm gradually decreases, while the characteristic absorption peak of the product p-aminophenol at 300 nm gradually increases. The conversion is completed after 155 s, and the reaction rate constant is 0.018 s. -1 This indicates that the microspheres have good catalytic performance.

[0096] Figure 7 The image shows the cycling performance test results of the lignin porous microspheres loaded with silver nanoparticles prepared in Example 1. 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 added back to the reaction system to catalyze the reduction of 4-NP by NaBH4. Each cycle experiment was conducted as described above (i.e.,...). Figure 6 The test was conducted under the same experimental conditions. As shown in the figure, after 5 cycles, the microspheres still completely catalyze p-nitrophenol within 7.5 minutes, indicating that the microspheres have good cycling performance.

[0097] To further investigate the catalytic ability of the microspheres of this invention, the concentrations of p-nitrophenol and sodium borohydride in the above reaction were each increased by 10 times (i.e., p-nitrophenol 0.1 mol / L, sodium borohydride 0.3 mol / L, volume the same as the above experimental conditions), and 20 mg of freshly prepared microspheres (Example 1) were added for testing. Figure 8 It can be seen that p-nitrophenol can be completely reduced within 30 minutes. This indicates that the microspheres of the present invention still have a good catalytic effect on high-concentration systems.

[0098] 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 metal nanoparticles, characterized in that, Includes the following steps: (1) Mix the lignin alkaline solution, crosslinking agent and chain extender evenly to obtain a lignin aqueous solution; (2) Mix the lignin aqueous solution and the inner oil phase containing surfactant, emulsify, and obtain O / W type primary emulsion; then mix the O / W type primary emulsion and the outer oil phase containing surfactant, emulsify, and obtain O / W / O type secondary emulsion; (3) The O / W / O type double emulsion was subjected to ultrasonic reaction. After the reaction was completed, the oil phase was removed and the mixture was washed to obtain lignin porous microspheres. (4) The lignin porous microspheres are suspended and dispersed in an aqueous solution of metal salt, and after heating or ultrasonic reaction, they are separated and dried to obtain lignin porous microspheres loaded with metal nanoparticles. The crosslinking agent in step (1) 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 (1) is at least one of ethylenediamine, hexamethylenediamine, polyetheramine, polyethyleneimine, triethylenetetramine, and diethylenetriamine; the amount of the chain extender is 0.1-15% of the lignin content; In step (4), the metal salt in the aqueous solution is at least one of AgNO3, HAuCl4, H2PtCl6 and PdCl2; In step (2), 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 (2), 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 metal nanoparticles according to claim 1, characterized in that, The ultrasonic power of the ultrasonic reaction in step (3) is 150-300 W; the reaction time is 30-60 min.

3. The method for preparing lignin porous microspheres loaded with metal nanoparticles according to claim 1, characterized in that, The mass ratio of the lignin aqueous solution and the inner oil phase containing surfactant in step (2) is 3:1 to 6:1; the mass ratio of the O / W type primary emulsion and the outer oil phase containing surfactant in step (2) is 1:3 to 1:5; The lignin alkaline solution in step (1) is obtained by adding lignin to an alkaline solution, wherein the concentration of the alkaline solution is 0.5–2.0 mol / L; and the mass fraction of lignin in the lignin alkaline solution is 40–65%. The internal oil phase containing surfactant described in step (2) consists of surfactant and oil phase, wherein the surfactant accounts for 0.1-2% of the total mass of the internal oil phase; The external oil phase containing surfactant in step (2) consists of surfactant and oil phase, wherein the surfactant accounts for 2 to 6% of the total mass of the external oil phase.

4. The method for preparing lignin porous microspheres loaded with metal nanoparticles according to claim 1, characterized in that, In step (4), the concentration of the metal salt in the aqueous solution is 10–100 mmol / L; The mass ratio of lignin porous microspheres to metal salt in step (4) is 1:2 to 1:

17.

5. The method for preparing lignin porous microspheres loaded with metal nanoparticles according to claim 1, characterized in that, In the lignin alkaline solution of step (1), the lignin is at least one of alkali lignin, solvent-based lignin, enzymatically hydrolyzed lignin, sodium lignin sulfonate, and amination-modified alkali lignin, amination-modified solvent-based lignin, amination-modified enzymatically hydrolyzed lignin, and amination-modified sodium lignin sulfonate. The lignin alkaline solution in step (1) is obtained by adding lignin to an alkaline solution, wherein the alkaline solution is at least one of sodium hydroxide solution and potassium hydroxide solution.

6. The method for preparing lignin porous microspheres loaded with metal nanoparticles according to claim 1, characterized in that, The heating reaction in step (4) is carried out at a temperature of 25-80°C for 0.5-12 hours; the ultrasonic reaction in step (4) is carried out at an ultrasonic power of 150-300W, a temperature of 30-50°C for 0.5-2 hours.

7. The method for preparing lignin porous microspheres loaded with metal nanoparticles according to claim 1, characterized in that, The emulsification conditions for the O / W type colostrum in step (2) 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 (3) is as follows: let it stand at normal pressure for 10 to 30 minutes and pour out the upper oil phase; the washing method is as follows: first wash with petroleum ether 3 to 6 times, and then transfer the microspheres to a Soxhlet extractor and extract with ethanol for 12 to 24 hours.

8. A lignin porous microsphere loaded with metal nanoparticles prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the lignin porous microspheres loaded with metal nanoparticles as described in claim 8 in the field of catalysis.

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