CN111495334A

CN111495334A - Cellulose adsorbent, preparation method and application thereof

Info

Publication number: CN111495334A
Application number: CN202010321715.2A
Authority: CN
Inventors: 杨卓鸿; 楚状状; 杨宇; 李朋松; 苏政
Original assignee: South China Agricultural University
Current assignee: South China Agricultural University
Priority date: 2020-04-22
Filing date: 2020-04-22
Publication date: 2020-08-07

Abstract

The invention belongs to the technical field of natural polymer modified materials, and relates to a preparation method of a cellulose adsorbent, which comprises the following steps: adding the oxidized wood into a polyethyleneimine-methanol solution for reaction, fully rinsing with water after the reaction is finished, then adding a glutaraldehyde solution for reaction, and obtaining the cellulose adsorbent after the reaction is finished. The invention also provides the cellulose adsorbent prepared by the preparation method and application thereof. The preparation method has strong controllability and simple operation, and the whole solution is prepared at room temperature, thereby being beneficial to large-scale production.

Description

Cellulose adsorbent, preparation method and application thereof

Technical Field

The invention belongs to the technical field of natural polymer modified materials, and relates to a cellulose adsorbent, and a preparation method and application thereof.

Background

The method for treating the wastewater containing the heavy metal ions mainly comprises a chemical precipitation method, an ion exchange method, a membrane separation method, an adsorption method and the like, wherein the adsorption method has the advantages of wide raw material source, simplicity in operation, high treatment efficiency and the like and becomes a research focus.

Cellulose is the most abundant green natural material in nature, and is considered as an indispensable raw material in the adsorbent due to its wide source, low price and excellent chemical modification ability. Wood, a carbon neutral biomass resource, contains about 45% cellulose. The traditional method is to remove lignin and hemicellulose, only leave wood cellulose, and then apply the cellulose to the heavy metal ion adsorption research. However, pure cellulose has almost no adsorption ability, and therefore, it is necessary to modify hydroxyl groups abundant in cellulose by chemical modification, thereby imparting some groups (amine groups, carboxyl groups, etc.) chelating heavy metal ions to cellulose, and thus to make it an adsorbent having excellent performance.

Patent CN110124623A discloses a preparation method of a modified corn straw cellulose adsorbent, which is prepared by using biomass waste corn straw through the steps of microcrystalline cellulose extraction, glycidyl methacrylate grafting, diethylenetriamine amination and the like, but the preparation process of the adsorbent needs to be carried out by crushing, ultrasound, deoxidization and the like, and the preparation method is complex and tedious in process, high in energy consumption and not beneficial to large-scale preparation.

Patent CN109289805A discloses that a nanocellulose composite aerogel adsorbent is prepared by mixing nanocellulose and a high molecular polymer (which may be polyethyleneimine) with a wet strength increasing performance, regulating a hydrogel structure by adopting a cyclic freezing-thawing-freezing mode, and realizing desorption and regeneration of the adsorbent by adopting a cyclic extrusion-absorption displacement-extrusion mode.

Disclosure of Invention

According to one aspect of the present invention, there is provided a method for preparing a cellulose adsorbent, comprising the steps of:

adding oxidized wood into a polyethyleneimine-methanol solution for reaction, fully rinsing with water after the reaction is finished, then adding a glutaraldehyde solution for reaction, and obtaining a cellulose adsorbent after the reaction is finished;

wherein the addition ratio of the oxidized wood, the polyethyleneimine-methanol solution and the glutaraldehyde solution is (1-5) g: (10-50) ml: (10-50) ml.

According to the preparation method, oxidized wood is crosslinked by glutaraldehyde, and polyethyleneimine is introduced into the wood, so that the cellulose adsorbent which is rich in amino groups, porous and good in compression performance is obtained.

The preparation method has strong controllability and simple operation, and the whole solution is prepared at room temperature, thereby being beneficial to large-scale production.

In some embodiments, the wood from which hemicellulose and lignin are removed is soaked in water having a pH of 8 to 12, 5 to 15mmol of sodium hypochlorite solution is added to 1g of wood for reaction for 2 to 5 hours, and then 0.1 to 0.5M hydrochloric acid solution is added to terminate the reaction, and then the wood is soaked with 0.1 to 0.5M hydrochloric acid solution to obtain oxidized wood.

In some embodiments, the wood from which hemicellulose and lignin are removed is obtained by the following method:

soaking wood in boiling water containing sodium hydroxide and sodium sulfite for 4-12 hr, taking out, and soaking in boiling sodium chlorite solution until the wood is white to obtain wood containing cellulose. Thus, the wood is subjected to alkali treatment and oxidation to remove hemicellulose and lignin, so that the wood containing cellulose is obtained.

In some embodiments, the polyethyleneimine-methanol solution is 0.1 to 6% by mass.

In some embodiments, the glutaraldehyde solution is 0.1-4% by weight of glutaraldehyde water solution.

In some embodiments, the method for preparing the cellulose adsorbent comprises the following specific steps:

(1) cutting 10-30g of wood into blocks, soaking the blocks in 300-500ml of boiling deionized water containing 10-20 g of sodium hydroxide and 5-10 g of sodium sulfite for reaction for 4-12h, taking out the blocks after the reaction is finished, then soaking the blocks in a boiling sodium chlorite solution with the mass fraction of 0.5-1% until the wood is white, fully rinsing the wood with deionized water after the reaction is finished, and freeze-drying the wood to obtain the wood containing cellulose;

(2) weighing the wood containing the cellulose obtained in the step (1), soaking the wood in deionized water with the pH value of 8-12, then adding 5-15mmol (calculated by 1g of wood containing the cellulose) of sodium hypochlorite solution, reacting for 2-5h, adding 0.1-0.5M hydrochloric acid solution to terminate the reaction, then soaking the wood in 0.1-0.5M hydrochloric acid solution, washing the wood with deionized water for several times, and freeze-drying to obtain oxidized wood;

(3) weighing 1-5 g of oxidized wood, adding 10-50 m L mass percent of 0-6% polyethyleneimine-methanol solution, reacting for 18-36 h, fully rinsing with deionized water after the reaction is finished, then adding 10-50 m L mass percent of 0.1-4% glutaraldehyde solution, reacting for 1-6 h at room temperature, fully rinsing with deionized water after the reaction is finished, and freeze-drying to obtain the cellulose adsorbent.

According to another aspect of the present invention, there is provided a cellulose adsorbent obtained by the above production method.

The cellulose adsorbent prepared by the method has the advantages of wide source, low price, high adsorption efficiency, large-scale cyclic adsorption and the like, and has important significance in the fields of biomass resource application to sewage treatment and the like.

Besides a large number of micropores, the cellulose microstructure also has micron-level holes which provide sufficient specific surface structures for the adsorbent and increase the contact area with the solution; the regularly arranged micropores also provide excellent compression-recovery capability for the adsorbent, and the mechanical compression performance of the adsorbent is slightly reduced after 100 times of cyclic compression tests.

In addition, the cellulose surface and the polyethyleneimine are connected by adopting covalent bonds, so that the polyethyleneimine crosslinking rate is high, and a large amount of amine groups are exposed on the surface of the adsorbent, so that adsorbed cations can easily reach chelating sites, and the adsorption sites such as the amine groups and the like are not easy to fall off from the adsorbent in the adsorption process; in the low pH environment, the amino group of the adsorbent for adsorbing heavy metal ions is easy to generate protonation, so that a large amount of heavy metal ions are separated from the adsorbent.

Therefore, the adsorbent has the advantages of being porous, compressible, strong in binding force between chelating sites and the adsorbent and the like, so that the heavy metal ions can be efficiently and quickly chelated, and the adsorption capacity and the cyclic adsorption capacity of the adsorbent are improved.

According to a further aspect of the present invention there is provided the use of a cellulose adsorbent in the treatment of wastewater containing heavy metal ions.

In some embodiments, the heavy metal ions include at least one of al (iii), cr (vi), ni (ii), co (ii), sn (ii), ag (i), fe (iii), cd (ii), pb (ii), mn (ii), zn (ii), and cu (ii).

The cellulose adsorbent is used for adsorbing heavy metal ions, and has positive reference value for widening the application of natural biomass resource wood and improving the added value of the wood; the biomass carbon neutral resource wood is used in the field of sewage treatment, and has positive promoting effects on expanding the types of adsorption materials, replacing commercial adsorbents and the like.

Drawings

FIG. 1 is an SEM photograph of a cellulose adsorbent prepared in example 1 of the present invention, with a scale of 50 μm.

FIG. 2 is an enlarged view of the internal structure of the frame in the SEM image of FIG. 1, with a scale of 1 μm.

FIG. 3 is a cyclic compressive stress-strain curve of the cellulose adsorbent of example 1 of the present invention.

FIG. 4 shows the adsorption capacity of the cellulose adsorbent of example 1 of the present invention for various heavy metal ions.

FIG. 5 shows a cellulose adsorbent and Cu according to example 1 of the present invention²⁺Influence of solution contact time on adsorption capacity.

FIG. 6 is a graph showing the results of a study on desorption of the cellulose adsorbent in example 1 of the present invention.

FIG. 7 is a graph showing the results of a study experiment of cyclic adsorption of the cellulose adsorbent of example 1 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples. It should be noted that "normal temperature" and "room temperature" in the present invention mean 15 ℃ to 30 ℃; unless otherwise specified, the reagents used in the present invention are commercially available.

The omitted operations in the invention are all the conventional operations in the field, such as 'freeze drying', namely drying by adopting the conventional freeze drying method for wood in the field; such as "deionized water at pH 10", is also obtained by adjusting the pH to about 10 using an alkaline reagent, which is conventional in the art, using techniques which are conventional in the art.

Example 1

The preparation method of the cellulose adsorbent comprises the following steps:

(1) cutting about 10g of wood into blocks, soaking the wood blocks in about 300ml of boiling deionized water containing about 10g of sodium hydroxide and about 5g of sodium sulfite, taking out the wood blocks after reacting for about 10 hours, then soaking the wood blocks in a boiling sodium chlorite solution with the mass fraction of about 0.5% until the wood blocks are whitened, fully rinsing the wood blocks with deionized water after the reaction is finished, and freeze-drying the rinsed wood blocks to obtain the wood blocks containing cellulose;

(2) weighing about 2g of the wood containing cellulose obtained in the step (1), soaking the wood in deionized water with the pH value of about 10, adding about 10mmol of sodium hypochlorite solution, reacting for about 2 hours, adding about 0.2M hydrochloric acid solution to stop the reaction, soaking the wood in about 0.2M hydrochloric acid solution, washing the wood with deionized water for a plurality of times, and freeze-drying to obtain oxidized wood;

(3) weighing about 1g of oxidized wood, adding about 10ml of polyethyleneimine-methanol solution with the mass fraction of about 4%, reacting for about 24 hours, fully rinsing with deionized water, then adding about 10ml of glutaraldehyde solution with the mass fraction of about 4%, reacting for about 1 hour at room temperature, fully rinsing with deionized water after the reaction is finished, and freeze-drying to obtain the cellulose adsorbent.

The cellulose adsorbent prepared in example 1 is subjected to electron microscope scanning, and SEM images thereof are shown in fig. 1 and fig. 2, wherein fig. 2 is an enlarged schematic view of a rectangular frame in fig. 1. FIGS. 1 and 2 show that, in addition to a large number of micropores, the microstructure of the cellulose adsorbent prepared in example 1 has micron-scale pores with a length of about 1-3 μm, which provides sufficient specific surface structure for the adsorbent and increases the contact area with the solution; furthermore, the relatively aligned micropores also provide excellent compression-recovery capability for the adsorbent, as shown in fig. 3, and the mechanical compression performance of the adsorbent is slightly reduced after 100 times of cyclic compression tests, which indicates the excellent compression-recovery capability of the adsorbent.

Example 2

(1) cutting about 30g of wood into blocks, soaking the wood blocks in about 500ml of boiling deionized water containing about 20g of sodium hydroxide and about 10g of sodium sulfite, taking out the wood blocks after reacting for about 12 hours, then soaking the wood blocks in a boiling sodium chlorite solution with the mass fraction of about 1% until the wood blocks are whitened, fully rinsing the wood blocks with deionized water after the reaction is finished, and freeze-drying the wood blocks to obtain the wood blocks containing cellulose;

(2) weighing about 3g of the wood containing the cellulose obtained in the step (1), soaking the wood in deionized water with the pH value of about 10, then adding about 30mmol of sodium hypochlorite solution, reacting for about 5 hours, then adding about 0.5M hydrochloric acid solution to stop the reaction, then soaking the wood in about 0.5M hydrochloric acid solution, washing the wood with deionized water for several times, and freeze-drying to obtain oxidized wood;

(3) weighing about 1g of oxidized wood, adding about 20ml of polyethyleneimine-methanol solution with the mass fraction of about 6%, fully rinsing with deionized water after reacting for about 24 hours, then adding about 20ml of glutaraldehyde solution with the mass fraction of about 4%, reacting for about 1 hour at room temperature, fully rinsing with deionized water after the reaction is finished, and freeze-drying to obtain the cellulose adsorbent.

The cellulose adsorbent prepared in example 2 was also subjected to electron microscope scanning, which also showed a large number of micropores and pores in the micrometer scale, and the SEM image thereof was omitted here for economy.

Comparative example 1

The preparation method of the cellulose adsorbent of the comparative example includes the following steps:

(1) cutting about 10g of wood into blocks, soaking the wood blocks in about 300ml of boiling deionized water containing about 10g of sodium hydroxide and about 5g of sodium sulfite, taking out the wood blocks after reacting for about 10 hours, then soaking the wood blocks in a boiling sodium chlorite solution with the mass fraction of about 0.5% until the wood blocks are whitened, fully rinsing the wood blocks with deionized water after the reaction is finished, and freeze-drying the wood blocks to obtain the wood blocks containing cellulose;

(2) weighing about 2g of the wood containing the cellulose obtained in the step (1), soaking the wood in deionized water with the pH value of about 10, adding about 10mmol of sodium hypochlorite solution, reacting for about 2 hours, adding about 0.2M hydrochloric acid solution to stop the reaction, soaking the wood in about 0.2M hydrochloric acid solution, washing the wood with deionized water for several times, and freeze-drying to obtain the oxidized wood adsorbent.

Comparative example 2

(2) weighing about 3g of the wood containing the cellulose obtained in the step (1), soaking the wood in deionized water with the pH value of about 10, then adding about 15mmol of sodium hypochlorite solution, reacting for about 2 hours, then adding about 0.2M hydrochloric acid solution to stop the reaction, then soaking the wood in about 0.2M hydrochloric acid solution, washing the wood with deionized water for several times, and freeze-drying to obtain oxidized wood;

(3) weighing about 1g of oxidized wood, adding about 10ml of polyethyleneimine-methanol solution with the mass fraction of about 4%, reacting for about 24 hours, fully rinsing with deionized water after the reaction is finished, and freeze-drying to obtain the cellulose adsorbent.

The adsorbents prepared in examples 1-2 and comparative examples 1-2 were used for Cu²⁺Solution adsorption with cross-linking rate of polyethyleneimine and Cu adsorption²⁺The adsorption results are shown in Table 1. Wherein:

comparative example 1 is wood not modified with polyethyleneimine, which has almost no adsorption capacity because there are no active groups in wood that attract heavy metal ions;

comparative example 2 wood, which was contacted only with polyethyleneimine and not crosslinked with glutaraldehyde, had a low polyethyleneimine crosslinking rate, resulting in a low adsorption capacity;

in the cellulose adsorbent of example 1, polyethyleneimine on the surface of the fibers is linked by covalent bonds, so that the crosslinking rate of polyethyleneimine is high, and the adsorption capacity is relatively strong;

in example 2, the cross-linking rate was higher than that in example 1, but the adsorption capacity was lower because the higher viscosity polyethyleneimine solution covered the wood surface, so that a small amount of polyethyleneimine entered the interior of the wood, and a large amount of polyethyleneimine accumulated on the wood surface to form a hard polymeric layer.

TABLE 1 cellulose adsorbent of the invention vs. Cu²⁺Adsorption capacity of

Product(s)	Cu²⁺Adsorption Capacity (mg/g)	Crosslinking ratio of polyethyleneimine (%)
			Example 1	91.56	50.35
Example 2	70.15	69
			Comparative example 1	1.09	0
Comparative example 2	16.99	9.32

The adsorption capacity of the cellulose adsorbent prepared in the examples of the present invention to heavy metals and the adsorption capacity of the cellulose adsorbent in cycles are described below by a series of experiments.

First, research on adsorption of different heavy metal ions by cellulose adsorbent

Separately prepared 1mg/m L Cu²⁺、Cr⁶⁺、Mn²⁺、Cd²⁺、Ni²⁺As an aqueous solution of heavy metal ions, 100mg of the cellulose adsorbent (PEI-NW) prepared in example 1 was put into 100m L of a heavy metal ion solution, and the adsorption capacity of the PEI-NW for different heavy metal ions was measured by sufficient absorption, as shown in FIG. 4.

As can be seen from FIG. 4, the cellulose adsorbent is on Cu²⁺、Cr⁶⁺、Mn²⁺、Cd²⁺、Ni²⁺The cellulose adsorbent prepared by the invention is a broad-spectrum adsorbent and can adsorb most heavy metal ions; and for Cr⁶⁺、Co³⁺、Ni²⁺、Ag⁺The adsorption capacity of the ions is more than 100 mg/g.

II, cellulose adsorbent to Cu²⁺The adsorption study of (2):

preparation of 1mg/m L Cu²⁺In an aqueous solution, 100mg of the cellulose adsorbent (PEI-NW) prepared in example 1 was charged with 100m L of Cu²⁺In the solution, adsorption studies were performed at 25 ℃. Sampling at adsorption time of 2, 4, 10, 30, 60, 120, 180, 240, 300, 360, 540min respectively for Cu determination²⁺The concentration, specific adsorption results are shown in fig. 5.

As can be seen from FIG. 5, the adsorption amount rapidly increased in the first 30min of the adsorption, and then slowly increased, and after 180min, the adsorption amount gradually reached equilibrium, and reached 93 mg/g.

As can be seen from the adsorption kinetics curve of the adsorbent provided by the patent application with the publication number of CN109289805A for Cu (II), the adsorption amount of the adsorbent reaches about 60mg/g when the adsorbent adsorbs Cu (II) for 100 min; as can be seen from FIG. 5, the adsorbent prepared in example 1 of the present invention adsorbed Cu (II) for 100min, and the adsorbed amount reached about 80 mg/g. Compared with the prior art, the adsorbent prepared in the embodiment 1 of the invention has high adsorption efficiency, and the adsorption efficiency is improved by 33.3 percent compared with the adsorption efficiency of the prior art.

The reason that the cellulose adsorbent prepared in example 1 of the present invention has high adsorption efficiency is that, since a large number of amine groups are exposed on the surface of the adsorbent, adsorbed cations easily reach chelating sites; in addition, the adsorbent has the advantages of porosity and compressibility, which are beneficial to the rapid chelation of heavy metal ions.

Third, cellulose adsorbent to Cu²⁺Study of desorption and cyclic adsorption capacity of (1):

preparation of 1mg/m L Cu²⁺In an aqueous solution, 100mg of the cellulose adsorbent (PEI-NW) prepared in example 1 was charged with 100m L of Cu²⁺In the solution, the adsorption was carried out sufficiently at 25 ℃. Putting the PEI-NW with balanced adsorption into a 1M hydrochloric acid solution, and performing desorption treatment, wherein the good compressibility of wood is utilized, and two treatment modes of extrusion-release and standing are respectively performed, and the desorption result is shown in FIG. 6; then, the compression-release desorption treatment was applied to the cyclic adsorption study of the adsorbent, and the adsorption capacity thereof was as shown in fig. 7 after 50 cycles of adsorption.

As shown in fig. 6, the desorption rate of 80% or more can be achieved by both desorption treatment methods until the end, but the cellulose adsorbent subjected to extrusion-release can basically achieve desorption equilibrium within 1 hour, and the desorption rate is significantly higher than that of the cellulose adsorbent subjected to standing desorption treatment, which indicates that extrusion-release is an effective desorption treatment method of the cellulose adsorbent of the present invention, and the cyclic adsorption efficiency can be improved in cyclic adsorption.

As shown in fig. 7, the adsorption capacity of the adsorbent of the present invention can reach more than 60% after 50 times of cyclic adsorption, which indicates that the cellulose adsorbent of the present invention has strong regeneration adsorption capacity; moreover, the heavy metal ion adsorption capacity of the adsorbent in the prior art in the patent CN109289805A is kept above 60-80% after 10 times of circulation, while the adsorbent in the invention is still kept in the range after 50 times of circulation, and compared with the two, the utilization rate of the adsorbent in the application is improved by 400%.

What has been described above are merely some embodiments of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the inventive concept thereof, and these changes and modifications can be made without departing from the spirit and scope of the invention.

Claims

1. The preparation method of the cellulose adsorbent is characterized by comprising the following steps:

the addition ratio of the oxidized wood, the polyethyleneimine-methanol solution and the glutaraldehyde solution is (1-5) g: (10-50) ml: (10-50) ml.

2. The method according to claim 1, wherein the polyethyleneimine-methanol solution is a 0.1 to 6 mass% polyethyleneimine-methanol solution.

3. The preparation method according to claim 2, wherein the glutaraldehyde solution is a 0.1-4% mass fraction aqueous solution of glutaraldehyde.

4. A method according to any one of claims 1-3, characterized in that the oxidized wood is obtained by:

soaking wood with hemicellulose and lignin removed in water with pH of 8-12, adding 5-15mmol sodium hypochlorite solution based on 1g wood, reacting for 2-5h, adding 0.1-0.5M hydrochloric acid solution to stop reaction, and soaking wood with 0.1-0.5M hydrochloric acid solution to obtain oxidized wood.

5. The method according to claim 4, wherein the wood from which hemicellulose and lignin are removed is obtained by the following method: soaking wood in boiling water containing sodium hydroxide and sodium sulfite for reaction for 4-12 hr, taking out, soaking in boiling sodium chlorite solution until the wood is white to obtain wood without hemicellulose and lignin.

6. A cellulose adsorbent produced by the production method according to any one of claims 1 to 5.

7. Use of the cellulose adsorbent according to claim 6 for the treatment of wastewater containing heavy metal ions.

8. The use of claim 7, wherein the heavy metal ions are at least one of Al (III), Cr (VI), Ni (II), Co (II), Sn (II), Ag (I), Fe (III), Cd (II), Pb (II), Mn (II), Zn (II), and Cu (II).