Preparation method and application of crosslinked cellulose-based porous rigid composite microspheres

Abstract

The invention discloses a preparation method of cross-linked cellulose-based porous rigid composite microspheres, which comprises the following steps: preparing cross-linked rigid cellulose porous microspheres, adding the porous cellulose microspheres into an oxidized multi-walled carbon nanotube particle dispersion liquid, adding a cross-linking agent under a stirring condition, and stirring to obtain the cross-linked cellulose-based porous rigid composite microspheres. And after the reaction is completed, carrying out post-treatment to obtain the crosslinked cellulose-based porous rigid composite microspheres. The invention also discloses a crosslinked cellulose-based porous rigid composite microsphere product and application thereof. Porous cellulose microspheres are used as a carrier. Compared with a polymer film, the porous cellulose microspheres provide more binding sites and better mechanical properties. The multi-walled carbon nanotubes (CNTs) with excellent thermal, electrical and mechanical properties are introduced at the same time, and an effective medium for adsorbing metal ions is provided. The cellulose / carbon nanotube porous composite microsphere provided by the invention has excellent adsorption performance on metal ions, and is an efficient biological adsorbent.

Description

Technical Field

[0001] The present invention relates to the technical field of cellulose microspheres, and particularly relates to a preparation method and application of cross-linked cellulose-based porous rigid composite microspheres. Background Art

[0002] With the increasing depletion of fossil resources and the increasingly serious environmental problems caused by the large-scale use of petroleum-based polymers, the preparation of polymer materials using bio-based raw materials instead of petroleum-based compound raw materials has attracted extensive attention. Cellulose has become an ideal raw material for bio-based polymer materials due to its rich sources, low price, excellent biodegradability, and easy modification. Cellulose and its derivative materials have been widely used in industrial fields such as fibers, papermaking, films, plastics, and biomedicine. Porous cellulose microspheres are natural polymer microspheres with diameters ranging from nanometers to micrometers and porous, network structures. Porous cellulose microspheres can provide a large specific surface area and a stable three-dimensional porous network structure, making it easy to composite with other functional materials. Therefore, the application potential of porous cellulose microspheres is extremely large.

[0003] Multi-walled carbon nanotubes (CNTs) have outstanding properties in many aspects: 1) Mechanical properties: They have extremely high elasticity and toughness and are currently the material with the highest specific strength in nature; 2) Electrical properties: Their conductivity is significantly better than that of materials such as graphene and carbon black, and the thinner the tube diameter and the longer the length, the better the conductivity; 3) Thermal conductivity: They have an extremely high thermal conductivity, and the thermal conductivity at room temperature is twice that of diamond. They have excellent axial thermal conductivity and poor radial thermal conductivity, and can be synthesized into anisotropic thermal conductive materials; 4) Chemical stability: They have acid and alkali resistance. Adding carbon nanotubes to polymer composites can improve the acid resistance and antioxidant properties of the material itself; 5) Excellent performance in embedding metal ions: The hollow lumen of carbon nanotubes, the gaps between tubes, the gaps between the middle layers of the tube walls, and various defects in the tube structure provide rich storage spaces and transportation channels for metal ions. Epichlorohydrin (ECH) is a colorless transparent liquid with an odor similar to chloroform. As an important chemical and pharmaceutical raw material and intermediate, it can be used as a common raw material and cross-linking agent in fields such as medicine, pesticides, food, plasticizers, and ion exchange resins.

[0004] With the rapid development of the global economy and the accelerating industrialization process, the pollution problem caused by heavy metal ion wastewater has become increasingly serious. Among them, common toxic heavy metal ions such as Hg 2+ 、As 3+ 、Cu 2+ 、Ni 2+ 、Cr 3+ 、Pb 2+ 、Cd 2+etc., even in small amounts, can cause serious consequences. Therefore, it is particularly urgent to find efficient and environmentally friendly methods for treating heavy metal wastewater. Currently, the main methods for treating heavy metals in water are: adsorption method, coagulation precipitation method, membrane separation technology, and biological methods, etc. The adsorption method has simple equipment and convenient operation, but it mainly focuses on the adsorption of single metal ions, and has little effect on the adsorption of multiple metal ions. The coagulation precipitation method has high treatment efficiency, but there are difficulties such as secondary pollution and high cost, and it is not suitable for treating low-concentration heavy metal wastewater. Although membrane separation technology is effective, energy-saving, convenient to operate, and has a wide range of applications, there are problems such as high cost, low domestic membrane output value, and easy membrane fouling. The advantage of the microbial method is that bacteria are widely sourced and more suitable for treating low-concentration sewage, but there are also problems such as low heavy metal removal ability and long removal time. The literature (Adsorption of Heavy Metals by Graphene Oxide / Cellulose Hydrogel Prepared from NaOH / Urea Aqueous Solution; Xiong Chen, Sukun Zhou, Liming Zhang, Tingting You and Feng Xu; Materials 2016, 9(7), 582) reported a method for preparing GO / cellulose hydrogel by cross-linking cellulose, graphene oxide (GO), and epichlorohydrin (ECH). GO / cellulose hydrogel has high adsorption performance for metal ions such as Zn 2+ 、Fe 3+ 、Pb 2+ etc., and is a new type of heavy metal biosorbent. However, the preparation time of the hydrogel is too long, the water absorption rate is slow during use, and GO will agglomerate during the preparation process, resulting in a decrease in the adsorption performance of the hydrogel, making this material not conducive to large-scale production. Summary of the Invention

[0005] The present invention aims at the deficiencies of the above technologies and provides a method for preparing cross-linked cellulose-based porous rigid composite microspheres. This method directly cross-links and fixes oxidized multi-walled carbon nanotube particles on the surface of tempered porous cellulose microspheres by using a cross-linking process to prepare a simple and novel cross-linked cellulose-based porous rigid composite microsphere, which has good performance in adsorbing metal ions.

[0006] The present invention also provides a cross-linked cellulose-based porous rigid composite microsphere, which has good performance in adsorbing metal ions.

[0007] The present invention also provides an application of a cross-linked cellulose-based porous rigid composite microsphere as a heavy metal ion adsorbent, which has good performance in adsorbing metal ions.

[0008] To achieve the above technical objectives and effects, the present invention is realized through the following technical solutions:

[0009] A preparation method of cross-linked cellulose-based porous rigid composite microspheres, comprising: subjecting porous cellulose microspheres to toughening treatment with cross-linking agent I to obtain rigid cellulose microspheres, adding the obtained rigid cellulose microspheres to an oxidized multi-walled carbon nanotube particle dispersion liquid, adding cross-linking agent II under stirring conditions, and performing post-treatment after the reaction to obtain the cross-linked cellulose-based porous rigid composite microspheres.

[0010] Using cross-linking agent I can achieve the preliminary toughening treatment of porous cellulose microspheres and ensure the initial stiffness of porous cellulose microspheres. Using cross-linking agent II can further improve the overall strength of the microspheres while realizing the loading of oxidized carbon nanotubes.

[0011] Preferably, the cross-linking agent I is any cross-linking agent that can achieve surface cross-linking of porous cellulose microspheres; the cross-linking agent I is selected from one or more of bis(2,3-epoxypropyl) ether, epichlorohydrin, and allyl glycidyl ether; the cross-linking agent II is any cross-linking agent that can achieve the fixation of oxidized multi-walled carbon nanotube particles on the surface of porous cellulose microspheres. Further preferably, the cross-linking agent II can be selected from one or more of bis(2,3-epoxypropyl) ether, epichlorohydrin (ECH), and 1,4-butanediol diglycidyl ether.

[0012] Preferably, the porous cellulose microspheres are obtained by the reverse suspension method.

[0013] Further preferably, the porous cellulose microspheres are obtained by the reverse suspension method, including: adding a cellulose solution to an immiscible oil-phase emulsion system, emulsifying to prepare a suspension with the oil phase as the continuous phase and the cellulose solution as the dispersed phase, performing solidification treatment on the dispersed phase in the suspension, and performing post-treatment to obtain porous cellulose microspheres.

[0014] Preferably, the volume ratio of the cellulose solution to the oil-phase emulsion system is 1:(3 - 5). More preferably, it is 1:(3 - 4.5); even more preferably, it is 1:(3 - 4); as a specific embodiment, the volume ratio of the cellulose solution to the oil-phase emulsion system is 1:4.

[0015] Preferably, the volume ratio of the emulsifier to the oil phase in the oil-phase emulsion system is (1 - 5):100. More preferably, the volume ratio of the emulsifier to the oil phase in the oil-phase emulsion system is (2 - 4.5):100. Even more preferably, the volume ratio of the emulsifier to the oil phase in the oil-phase emulsion system is (2.5 - 3.5):100.

[0016] Preferably, the oil-phase emulsion system consists of an emulsifier and an oil phase; the oil phase is selected from one or more of vegetable oil, liquid paraffin, xylene (o-xylene, m-xylene, etc.); the emulsifier is selected from one or more of Span60, Span80, Span80, Tween80.

[0017] Preferably, the cellulose solution is added to the immiscible oil-phase emulsion system, and stirred and emulsified at a stirring speed of 500-2000 r / min and at room temperature for 3-6 h to obtain the suspension with the oil phase as the continuous phase and the cellulose solution as the dispersed phase.

[0018] Preferably, the pH value of the suspension is adjusted to neutral with dilute hydrochloric acid or ethanol is added to achieve the solidification; after the solidification is completed, the post-treatment is as follows: the solidified system is allowed to stand and layered, and the oil phase is washed with water and recycled; the cellulose microspheres separated from the aqueous phase are washed to obtain the final porous cellulose microspheres.

[0019] Specifically, a method for preparing porous cellulose microspheres includes:

[0020] (1) Dissolve the emulsifier (such as Span80) in the oil phase (such as liquid paraffin) (the volume ratio of the emulsifier to the oil phase is preferably 2.5-3.5:100), stir at a speed of 500-2000 r / min for 10-60 min, and then add a certain amount of the above-mentioned cellulose solution within 1 h. The obtained suspension is stirred and emulsified at a stirring speed of 500-2000 r / min and at room temperature for 3-6 h;

[0021] (2) Under the above conditions, add dilute hydrochloric acid (5-15%, preferably 10%) dropwise to adjust the pH value to 6-8 (preferably 7), and the suspension solidifies to form regenerated cellulose microspheres; allow to stand, and the mixture system is divided into two layers: the upper layer is the liquid paraffin organic phase which can be recycled by washing with water, and the lower aqueous phase is centrifugally washed several times (such as 2-5 times) with ethanol and deionized water to obtain the regenerated cellulose microspheres.

[0022] Preferably, the cellulose is natural cellulose (such as crop residues, etc.), and the preparation method of the cellulose solution is as follows: put the cellulose into the pre-cooled sodium hydroxide-urea aqueous solution, stir at 350-450 r / min for 5-15 min, then centrifuge and degas at 2800-5000 r / min for 10-20 min at room temperature, and place the cellulose solution in an ice-water bath after centrifugation. Of course, other celluloses other than natural cellulose can also be used in the present invention. When using other types of celluloses, the corresponding dissolution method can be selected, and the purpose is to obtain a homogeneous cellulose solution.

[0023] Preferably, the pre-cooled sodium hydroxide-urea aqueous solution is prepared by the following method: Weigh a certain amount of sodium hydroxide, urea, and water (mass ratio is 5-8:10-14:78-82), mix them evenly, and then place them in a refrigerator and pre-cool to -18 to 10 °C.

[0024] Specifically, the preparation method of the cellulose solution includes:

[0025] (1) Weigh a certain amount of sodium hydroxide, urea, and water (mass ratio is 5-8:10-14:78-82, preferably 7:12:81), mix them evenly, and then place them in a refrigerator and pre-cool to -18 to 10 °C.

[0026] (2) Quickly put the cellulose sample into the pre-cooled solution, stir at 350-450 r / min for 5-15 min, and then centrifuge and degas at 2800-5000 r / min for 10-20 min at room temperature. After centrifugation, place the cellulose solution in an ice-water bath.

[0027] Preferably, the concentration of cellulose in the cellulose solution is 2-10%; more preferably 3-8%, and even more preferably 3-5%. As a specific embodiment, the mass ratio of cellulose to the pre-cooled sodium hydroxide-urea aqueous solution is 4:96.

[0028] Preferably, the process of toughening the porous cellulose microspheres with crosslinking agent I includes: Suspending the porous cellulose microspheres in deionized water, with the mass ratio of microspheres to water being 2-4:1, heating to 30-40 °C, adding the NaOH solution and crosslinking agent I to the reaction system, stirring until the reaction is complete, and then performing post-treatment to obtain the rigid cellulose microspheres.

[0029] Furthermore: Weigh the prepared porous cellulose microspheres and suspend the microspheres in deionized water, with the mass ratio of microspheres to water being 2-4:1 (preferably 3:1). Transfer this mixed system to a reactor with a water bath and stirring, heat to 30-40 °C (preferably 35 °C), add a 0.5-2 M NaOH solution and crosslinking agent I (ECH) to the reaction system, and stir for 0.5-2 hours. Centrifuge and wash several times with ethanol and deionized water respectively to obtain the rigid cellulose microspheres.

[0030] The added molar amount of crosslinking agent I is 10-30 mmol / g of the mass of the porous cellulose microspheres. The added volume of the NaOH solution is 1-3 mL / g of the mass of the porous cellulose microspheres.

[0031] Preferably, the oxidized multi-walled carbon nanotube particle dispersion is obtained by the following method: Add oxidized CNTs nanoparticles to deionized water and perform ultrasonic treatment on the solution for 0.5-2 hours.

[0032] Preferably, the mass percentage content of the oxidized multi-walled carbon nanotube particles in the oxidized multi-walled carbon nanotube particle dispersion is 1-30%; more preferably 1-25%; even more preferably 3-20%.

[0033] Preferably, the mass ratio of the rigid cellulose microspheres to the oxidized multi-walled carbon nanotube particles is 1:(1-30); more preferably 1:(1-25); even more preferably 1:(3-25); specifically preferably 1:(3-15).

[0034] Preferably, the molar amount of cross-linking agent II added is 65-85 mmol / g of the mass of the rigid cellulose microspheres; more preferably 70-80 mmol / g.

[0035] Preferably, the oxidized multi-walled carbon nanotube particles are obtained by oxidizing multi-walled carbon nanotubes with a mixture of sulfuric acid and nitric acid, followed by ultrasonic treatment at 50-70 °C for 2-4 hours, and then washing and drying. Specifically, it includes:

[0036] (1) Oxidize the carbon nanotubes with a mixture of sulfuric acid and nitric acid: Disperse CNTs (multi-walled carbon nanotubes) in sulfuric acid and nitric acid (3:1; v / v), and perform ultrasonic treatment in an ultrasonic bath at 50-70 °C for 2-4 h; the mass-volume ratio of CNTs to the sulfuric acid and nitric acid mixture is 1-10 / 100 (g / ml);

[0037] (2) Centrifuge and wash the oxidized CNTs with ethanol and deionized water at 2000-6000 rpm (preferably 3000-5000 rpm) for 15-25 min;

[0038] (3) Dry the centrifuged and washed oxidized CNT nanoparticles in an oven at 40-60 °C for 10-15 h to obtain the oxidized multi-walled carbon nanotube particles.

[0039] As a specifically preferred scheme, the preparation method of the cross-linked cellulose-based porous rigid composite microspheres includes:

[0040] (1) Add oxidized CNT nanoparticles to deionized water (the weight percentage of oxidized CNT nanoparticles in the dispersion is preferably 3-20%), and perform ultrasonic treatment on the solution for 0.5-2 hours;

[0041] (2) Add the prepared porous tempered cellulose microspheres to the oxidized CNTs dispersion, stir at 20 - 40 °C (preferably 30 °C) for 0.5 - 2 h (preferably 1 h), and then gradually add 3 - 10 mL of crosslinking agent II (such as ECH) dropwise to the CNTs / cellulose microsphere mixture. After the feeding of crosslinking agent II (ECH) is completed, stir and react the obtained mixture at 20 - 40 °C (preferably 30 °C) for 0.5 - 2 h (preferably 1 h).

[0042] (3) Centrifuge and wash these microsphere samples with ethanol and deionized water respectively, and store them by cooling and drying or store them in a 20% ethanol solution at 0 - 5 °C.

[0043] As a specific optimization scheme, a preparation method of crosslinked cellulose-based porous rigid composite microspheres includes:

[0044] A preparation method of crosslinked cellulose-based porous rigid composite microspheres includes the following steps:

[0045] (1) Functionalization of multi-walled carbon nanotubes

[0046] 1. Oxidize the carbon nanotubes with a mixture of sulfuric acid and nitric acid: Disperse 0.1 - 1.0 g of CNTs in 100 mL of sulfuric acid and nitric acid (3:1; v / v), and ultrasonically treat them in an ultrasonic bath at 50 - 70 °C for 2 - 4 h; in this step, the addition amounts of CNTs, sulfuric acid and nitric acid can also be adjusted proportionally as needed;

[0047] 2. Obtain the oxidized CNTs by centrifuging at 5000 rpm for 15 - 25 min, and then dry them in an oven at 50 - 70 °C for 10 - 15 h;

[0048] 3. Then, add 0.1 - 1.0 g of oxidized CNTs to 100 mL of deionized water, and ultrasonically treat them at 40 - 60 °C for 1 - 3 h to uniformly disperse the oxidized CNTs.

[0049] 4. Obtain the functionalized CNTs nanoparticles by centrifugation, and dry them in an oven at 40 - 60 °C for 10 - 15 h.

[0050] (2) Preparation of cellulose solution

[0051] 5. Weigh a certain amount of sodium hydroxide, urea, and water (mass ratio 5 - 8:10 - 14:78 - 82), mix them evenly, and pre-cool them in a refrigerator to -18 - 10 °C.

[0052] 6. Quickly place the cellulose sample into the pre-cooled solution. After stirring at 300 - 500 r / min for 5 - 15 min, centrifuge at 2800 - 5000 r / min for 10 - 20 min at room temperature to degas. After centrifugation, place the cellulose solution in an ice-water bath.

[0053] (3) Preparation of cellulose / carbon nanotube nanoporous microspheres

[0054] 7. Dissolve 6 mL of Span80 in 200 mL of liquid paraffin and stir at a speed of 500 - 2000 r / min for 10 - 60 min. Then add a certain amount of the above-mentioned cellulose solution within 1 h. Stir and emulsify the obtained suspension at a stirring speed of 500 - 2000 r / min and at room temperature for 3 - 6 h.

[0055] 8. Under the above conditions, add 10% dilute hydrochloric acid dropwise to adjust the pH to 7.0, and the suspension solidifies to form regenerated cellulose microspheres. Let it stand, and the mixture system is divided into two layers: the upper layer is the liquid paraffin organic phase, which can be recycled by washing with water, and the lower aqueous phase is centrifugally washed 3 times with ethanol and deionized water respectively to obtain regenerated cellulose microspheres;

[0056] 9. Improve the mechanical properties of the microspheres through several additional steps of extensive cross-linking using, for example, epichlorohydrin in the presence of sodium hydroxide to obtain rigid porous cellulose microspheres. Improving the rigidity of the microspheres can also be achieved by coupling allyl glycidyl ether (AGE) in the presence of sodium hydroxide, and then inactivating and hydrolyzing.

[0057] 10. Take three different mass fractions (wt%) of CNTs nanoparticles and add them to 100 mL of deionized water, and ultrasonically treat the solution for 0.5 - 2 hours;

[0058] 11. Respectively take 1 g of the rigid porous cellulose microspheres prepared in the above steps and add them to the CNTs solutions with three mass fractions. Stir at 30 °C for 1 h, and then gradually add 3 - 10 mL of the cross-linking agent dropwise to the CNTs / cellulose microsphere mixture. After the cross-linking agent feeding is completed, stir and react the obtained mixture at 30 °C for 1 h.

[0059] 12. Centrifugally wash these microsphere specimens 3 times with ethanol and deionized water respectively, and store them by freeze-drying or store them in a 20% ethanol solution at 0 - 5 °C, and label them as 3%

[0060] (RC / CNTs-1), 5% (RC / CNTs-2) and 10% (RC / CNTs-3).

[0061] 13. Store these microsphere specimens by freeze-drying or store them in a 20% ethanol solution at 0 - 5 °C.

[0062] The present invention also provides a crosslinked cellulose-based porous rigid composite microsphere, which is prepared by the preparation method described in any one of the above technical solutions.

[0063] The present invention also provides an application of the crosslinked cellulose-based porous rigid composite microsphere obtained by any one of the above technical solutions as a heavy metal adsorbent.

[0064] The crosslinked cellulose-based porous rigid composite microsphere of the present invention as a heavy metal adsorbent can be used in various water bodies containing heavy metal ions, such as various wastewaters, etc., to achieve the removal of heavy metal ions. The heavy metal ions include but are not limited to Hg 2+ , As 3+ , Cu 2+ , Ni 2+ , Cr 3+ , Pb 2+ , Cd 2+ etc., or a mixture of one or more of them; as a further preference, the heavy metal ions include Ni 2+ and Pb 2+ .

[0065] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0066] The present invention prepares porous cellulose microspheres anchored with multi-walled carbon nanotubes by the reverse suspension method. The porous cellulose microspheres as carriers improve the biocompatibility, biodegradability, hydrophilicity and moisture retention of the polymer microspheres. Compared with polymer films, the porous cellulose microspheres have a higher specific surface area and better mechanical properties, and can provide more binding sites. The present invention also introduces multi-walled carbon nanotubes (CNTs) with excellent thermal, electrical and mechanical properties, providing an effective medium for adsorbing metal ions. In order to solve the problems of low adsorption capacity, slow adsorption rate, unstable structure and poor adsorption ability existing in traditional cellulose-based heavy metal adsorbents and improve the adsorption effect on heavy metal ions, the cellulose / carbon nanotube porous composite microspheres provided by the present invention have excellent adsorption performance for metal ions and are an efficient biosorbent. Description of the Drawings

[0067] Figure 1 is a flow chart of the preparation method of the crosslinked cellulose-based porous rigid composite microsphere.

[0068] Figure 2 is a scanning electron micrograph of the crosslinked cellulose-based porous rigid composite microsphere (CNTs content is 3 wt%).

[0069] Figure 3 is a graph of the adsorption capacity of the crosslinked cellulose-based porous rigid composite microsphere for heavy metal ions. Detailed Embodiments

[0070] The following specific implementation examples are used to further illustrate the method described in the present invention, but do not limit the present invention.

[0071] Example 1

[0072] As Figure 1 shown, carbon nanotubes were oxidized with a mixture of sulfuric acid and nitric acid: 3.0 g of CNTs (purchased from Aladdin) were dispersed in 100 mL of sulfuric acid and nitric acid (3:1; v / v), and ultrasonically treated in an ultrasonic bath at 60 °C for 3 h; then the oxidized CNTs were centrifugally washed with ethanol and deionized water at 4000 rpm for 15 - 25 min respectively. The centrifugally washed CNT nanoparticles were dried in an oven at 40 - 60 °C for 10 - 15 h.

[0073] A certain amount of sodium hydroxide, urea, and water (mass ratio 7:12:81) were mixed evenly and pre-cooled to -12 °C in a refrigerator. A cellulose (bagasse, industrial grade) sample was quickly put into the pre-cooled solution (cellulose mass fraction 4 wt%), stirred at 400 r / min for 10 min, and then centrifuged at 4000 r / min for 15 min at room temperature to degas. After centrifugation, the cellulose solution was placed in an ice-water bath.

[0074] 6 mL of Span80 was dissolved in 200 mL of liquid paraffin and stirred at 500 r / min for 30 min, and then a certain amount of the above cellulose solution (water-oil ratio 1:4) was added within 1 h. The resulting suspension was stirred and emulsified at 500 r / min and at room temperature for 3 h. 10% dilute hydrochloric acid was added dropwise to adjust the pH to 7.0, and the suspension solidified to form regenerated cellulose microspheres. After standing, the mixture system was divided into two layers: the upper layer was the liquid paraffin organic phase which could be recycled by washing with water, and the lower aqueous phase was centrifugally washed 3 times with ethanol and deionized water respectively to obtain regenerated cellulose microspheres.

[0075] 2 g of cellulose microspheres were weighed and the microspheres were suspended in deionized water, with the mass ratio of microspheres to water being 3:1. The mixed system was transferred to a reactor with a water bath and stirring, heated to 35 °C, and 3 mL each of 1 M NaOH solution and cross-linking agent ECH were added to the reaction system and stirred for 1 h. They were centrifugally washed 3 times with ethanol and deionized water respectively to obtain rigid cellulose microspheres;

[0076] Add 3 wt% of CNTs nanoparticles to 100 mL of deionized water, and ultrasonically treat the solution for 1 hour; take 1 g of the porous cellulose microspheres prepared in the above step and add them to the 3 wt% CNTs solution, stir at 30 °C for 1 h, and then add 6 mL of ECH as a crosslinking agent dropwise to the CNTs / cellulose microsphere mixture. After the ECH feeding is completed, stir and react the obtained mixture at 30 °C for 1 h. Centrifuge and wash these microsphere samples three times with ethanol and deionized water respectively, and store them by freeze-drying or store them in a 20% ethanol solution at 0 - 5 °C, labeled as 3% (RC / CNTs-1), and the scanning electron micrograph is added Figure 2 。

[0077] The adsorption performance of RC / CNTs-1 porous microspheres for Ni 2+ and Pb 2+ was determined by the static adsorption method: Weigh 0.5 g of the RC / CNT porous microspheres and place them in a 250 mL conical flask, and add an aqueous solution of Ni 2+ and Pb 2+ with a concentration of 100 mg / g to the flask, shake it on an oscillator at a speed of 170 r / min for a certain period of time, separate the supernatant and measure the concentration of heavy metal ions in it. The pH of the measured solution is 5.0, the temperature is 25 °C, and the stirring time is 12 h. The results are shown in Figure 3 。

[0078] Example 2

[0079] Oxidize the carbon nanotubes with a mixture of sulfuric acid and nitric acid: Disperse 5.0 g of CNTs (purchased from Aladdin) in 100 mL of sulfuric acid and nitric acid (3:1; v / v), and ultrasonically treat it in an ultrasonic bath at 60 °C for 3 h; then centrifuge and wash the oxidized CNTs with ethanol and deionized water at 4000 rpm for 15 - 25 min respectively. Dry the centrifuged and washed CNTs nanoparticles in an oven at 40 - 60 °C for 10 - 15 h.

[0080] Weigh a certain amount of sodium hydroxide, urea, and water (mass ratio of 7∶12∶81), mix them evenly and pre-cool them to -12 °C in a refrigerator. Quickly put the cellulose (bagasse, industrial grade) sample into the pre-cooled solution (cellulose mass fraction is 4 wt%), stir at 400 r / min for 10 min, and then centrifuge and degas at 4000 r / min for 15 min at room temperature. After centrifugation, place the cellulose solution in an ice-water bath.

[0081] Dissolve 6 mL of Span80 in 200 mL of liquid paraffin and stir at a speed of 500 r / min for 30 min. Then, add a certain amount of the above-mentioned cellulose solution (water-oil ratio 1:3) within 1 h. The obtained suspension is stirred and emulsified at a stirring speed of 500 r / min and room temperature for 3 h. Add 10% dilute hydrochloric acid dropwise to adjust the pH to 7.0, and the suspension solidifies to form regenerated cellulose microspheres. Let it stand, and the mixture system is divided into two layers: the upper layer is the liquid paraffin organic phase, which can be recycled by washing with water, and the lower aqueous phase is centrifugally washed 3 times with ethanol and deionized water respectively to obtain regenerated cellulose microspheres;

[0082] Weigh 2 g of cellulose microspheres and suspend the microspheres in deionized water with a mass ratio of the microspheres to water of 3:1. Transfer this mixed system to a reactor with a water bath and stirring, heat to 35 °C, add 3 mL each of 1 M NaOH solution and crosslinking agent ECH to the reaction system, and stir for 1 h. Centrifugally wash 3 times with ethanol and deionized water respectively to obtain rigid cellulose microspheres;

[0083] Add 5 wt% of CNTs nanoparticles to 100 mL of deionized water and ultrasonically treat the solution for 1 h; take 1 g of the porous cellulose microspheres prepared in the above step and add them to the 5 wt% CNTs solution, stir at 30 °C for 1 h, and then gradually add 6 mL of ECH as a crosslinking agent dropwise to the CNTs / cellulose microsphere mixture. After the addition of ECH is completed, stir and react the obtained mixture at 30 °C for 1 h. Centrifugally wash these microsphere samples 3 times with ethanol and deionized water respectively, and store them by cooling and drying or store them in a 20% ethanol solution at 0 - 5 °C, labeled as 5% (RC / CNTs-2).

[0084] The adsorption performance of RC / CNTs-2 porous microspheres for Ni 2+ and Pb 2+ was measured by the static adsorption method: Weigh 0.5 g of RC / CNTs porous microspheres and place them in a 250 mL conical flask, add an aqueous solution of Ni 2+ and Pb 2+ at 100 mg / g to the flask, oscillate at a speed of 170 r / min on an oscillator for a certain time, separate the supernatant and measure the concentration of heavy metal ions in it. The pH of the measured solution is 5.0, the temperature is 25 °C, and the stirring time is 12 h. The results are shown in Figure 3 .

[0085] Example 3

[0086] Oxidation of carbon nanotubes with a mixture of sulfuric acid and nitric acid: 10.0 g of CNTs (purchased from Aladdin) were dispersed in 100 mL of sulfuric acid and nitric acid (3:1; v / v), and ultrasonically treated in an ultrasonic bath at 60 °C for 3 h; then the oxidized CNTs were centrifugally washed with ethanol and deionized water at 4000 rpm for 15 - 25 min respectively. The centrifugally washed CNT nanoparticles were dried in an oven at 40 - 60 °C for 10 - 15 h.

[0087] Weigh a certain amount of sodium hydroxide, urea, and water (mass ratio 7∶12∶81), mix them evenly, and pre-cool in a refrigerator to -12 °C. Quickly put the cellulose (bagasse, industrial grade) sample into the pre-cooled solution (cellulose mass fraction 4 wt%), stir at 400 r / min for 10 min, and then centrifuge at 4000 r / min for 15 min at room temperature for degassing. After centrifugation, place the cellulose solution in an ice-water bath.

[0088] Dissolve 6 mL of Span80 in 200 mL of liquid paraffin, stir at a speed of 500 r / min for 30 min, and then add a certain amount of the above cellulose solution (water-oil ratio 1:4.5) within 1 h. The resulting suspension was stirred and emulsified at a stirring speed of 500 r / min and at room temperature for 3 h. Add 10% dilute hydrochloric acid dropwise to adjust the pH to 7.0, and the suspension solidifies to form regenerated cellulose microspheres. Let it stand, and the mixture system is divided into two layers: the upper layer is the liquid paraffin organic phase, which can be recycled by washing with water, and the lower aqueous phase is centrifugally washed 3 times with ethanol and deionized water respectively to obtain regenerated cellulose microspheres;

[0089] Weigh 2 g of cellulose microspheres and suspend the microspheres in deionized water, with the mass ratio of the microspheres to water being 3:1. Transfer this mixed system to a reactor with a water bath and stirring, heat to 35 °C, take 3 mL each of 1 M NaOH solution and crosslinking agent ECH and add them to the reaction system, and stir for 1 h. Centrifugally wash 3 times with ethanol and deionized water respectively to obtain rigid cellulose microspheres;

[0090] Take 10 wt% of CNT nanoparticles and add them to 100 mL of deionized water, and ultrasonically treat the solution for 1 h; take 1 g of the porous cellulose microspheres prepared in the above step and add them to the 10 wt% CNT solution, stir at 30 °C for 1 h, and then gradually add 6 mL of ECH as a crosslinking agent dropwise to the CNT / cellulose microsphere mixture. After the addition of ECH is completed, stir and react the resulting mixture at 30 °C for 1 h. Centrifugally wash these microsphere samples 3 times with ethanol and deionized water respectively, and store them by cooling and drying or store them in a 20% ethanol solution at 0 - 5 °C, labeled as 10% (RC / CNTs-3).

[0091] The adsorption performance of Ni 2+ and Pb 2+ onto RC / CNTs-3 porous microspheres was determined by static adsorption method: 0.5 g of RC / CNTs porous microspheres was weighed and placed in a 250 mL conical flask, and an aqueous solution containing 100 mg / g of Ni 2+ and Pb 2+ was added to the flask. The mixture was shaken on an oscillator at a speed of 170 r / min for a certain time, and then the supernatant was separated and the concentration of heavy metal ions in it was measured. The pH of the measured solution was 5.0, the temperature was 25 °C, and the stirring time was 12 h. The results are shown in Figure 3 .

Claims

1. A method for preparing cross-linked cellulose-based porous rigid composite microspheres, characterized in that: include: The porous cellulose microspheres are tempered with a crosslinking agent I to obtain rigid cellulose microspheres, the obtained rigid cellulose microspheres are added to a dispersion of oxidized multi-walled carbon nanotube particles, and a crosslinking agent II is added under stirring conditions. After the reaction is completed, post-treatment is performed to obtain the cross-linked cellulose-based porous rigid composite microspheres.

2. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 1, characterized in that: The porous cellulose microspheres are obtained by a reverse suspension method.

3. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 2, characterized in that: The porous cellulose microspheres are obtained by the following method, including: adding a cellulose solution into an immiscible oil phase emulsification system, emulsifying, preparing a suspension with the oil phase as a continuous phase and the cellulose solution as a dispersed phase, solidifying the dispersed phase in the suspension, and post-treating to obtain porous cellulose microspheres.

4. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 3, characterized in that: The volume ratio of the cellulose solution to the oil phase emulsified system is 1:(3-5).

5. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 3 or 4, characterized in that: The oil phase emulsification system consists of an emulsifier and an oil phase; the oil phase is selected from one or more of vegetable oil, liquid paraffin, and xylene; the emulsifier is selected from one or more of Span60, Span80, Span80, and Tween80; the volume ratio of the emulsifier to the oil phase in the oil phase emulsification system is (1-5):

100.

6. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 3, characterized in that: The cellulose solution is added to the immiscible oil phase emulsification system, and the mixture is stirred and emulsified at a stirring speed of 500 to 2000 r / min and room temperature for 3 to 6 hours to obtain the suspension with the oil phase as the continuous phase and the cellulose solution as the dispersed phase.

7. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 1, characterized in that: The method for preparing the rigid cellulose microspheres is as follows: suspending porous cellulose microspheres in deionized water, with a mass ratio of microspheres to water of 2 to 4:1, heating to 30 to 40° C., adding NaOH solution and crosslinking agent I to the reaction system, stirring until the reaction is completed, and post-processing to obtain the rigid cellulose microspheres.

8. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 1, characterized in that: The oxidized multi-walled carbon nanotube particle dispersion is obtained by the following method: adding oxidized CNTs nanoparticles into deionized water, subjecting the solution to ultrasonic treatment for 0.5 to 2 hours, and obtaining the oxidized multi-walled carbon nanotube particle dispersion; in the oxidized multi-walled carbon nanotube particle dispersion, the mass percentage content of the oxidized multi-walled carbon nanotube particles is 1 to 30%; the mass ratio of the rigid cellulose microspheres to the oxidized multi-walled carbon nanotube particles is 1:(1 to 30).

9. The method for preparing cross-linked cellulose-based porous rigid composite microspheres according to claim 1, characterized in that: The crosslinking agent I is selected from one or more of dioxirane, epichlorohydrin, and allyl glycidyl ether; the crosslinking agent II is selected from one or more of dioxirane, epichlorohydrin, and 1,4-butanediol diglycidyl ether.

10. A cross-linked cellulose-based porous rigid composite microsphere, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 9.

11. Use of the cross-linked cellulose-based porous rigid composite microspheres according to claim 10 as a heavy metal ion adsorbent.

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