Nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material as well as preparation method and application thereof

Abstract

The invention relates to a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material and a preparation method and application thereof.The preparation method comprises the steps that S1, a mixed solution of cellulose nanocrystal suspension and acrylic acid is subjected to continuous magnetic stirring, and a uniformly-dispersed cellulose nanocrystal / acrylic acid mixture is formed; s2, adding an N, N '-methylene bisacrylamide cross-linking agent into the dispersion liquid obtained in the step S1, and continuously stirring; s3, nano zero-valent iron is added into the dispersion liquid obtained in the step S2, and stirring is continued; s4, slowly adding an APS initiator into the dispersion liquid obtained in the step S3 until the color of the mixture is changed and a semi-solidified colloid is formed; and S5, drying the semi-gel mixture obtained in the step S4 to obtain the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material. The nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material has low toxicity, uniformity and biodegradability, has a large number of adsorption sites, and can efficiently adsorb and remove diclofenac in wastewater.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a nano-iron cross-linked cellulose nano-crystal / polyacrylic acid composite material and a preparation method and application thereof. Background Art

[0002] Diclofenac is one of the most widely used nonsteroidal anti-inflammatory drugs in the world and has potential environmental and health risks. Conventional drinking water and sewage treatment processes are not ideal for the removal of diclofenac. Given its widespread distribution and potential ecological hazards, it is necessary to conduct research on the adsorption treatment technology of diclofenac in water. Traditional polyacrylic acid-based hydrogels are effective adsorbents for diclofenac. However, low mechanical strength and toxicity limit their application. The method of cross-linking biomass polymers can not only enrich the cross-linked network and thus improve the rigidity of the hydrogel, but also increase its green sustainability and biocompatibility while improving the adsorption performance of the hydrogel. Nanocellulose crystals are one of the best candidates for forming cross-linked hydrogels because of their unique nanostructure, abundant hydroxyl and sulfonic acid groups, and the strong 3D hydrophilic network formed by cross-linking with polyacrylic acid (PAA) creates a feasible diffusion pathway for the adsorption of diclofenac in water.

[0003] However, pure cellulose nanocrystal / polyacrylic acid hydrogel still has the problem of insufficient binding sites, resulting in limited targeted adsorption of diclofenac, and the adsorption capacity needs to be improved. Metal ion doping can effectively improve this problem. Metal ions can form dynamic reversible coordination bonds in hydrogels with negatively charged groups, thereby increasing the crosslinking density and structural integrity of the hydrogel. Therefore, incorporating metal ions into hydrogels is the key to activating this multi-component composite material. Among the many metal ions, iron is widely used in the construction of nanomaterials due to its low cost, high earth abundance, and strong coordination ability. However, iron ions can directly activate polymers to undergo polymerization reactions, resulting in uneven crosslinking of the formed hydrogel. In order to solve this problem, nano zero-valent iron can be used as a new crosslinking agent to crosslink hydrogels by slowly releasing iron ions in situ. Nano zero-valent iron has a small size (20-100nm), a large specific surface area, high activity, and has Fe 0 The "core-shell" structure is a core with iron oxide as the layer. In water, iron ions can be slowly released by nano zero-valent iron and react with oxygen in water to form iron oxide. Therefore, nano zero-valent iron can be used as a functional cross-linking agent for cellulose nanocrystal / polyacrylic acid hydrogel, so that iron ions are slowly released and orderly cross-linked with the negatively charged groups on the cellulose nanocrystal / polyacrylic acid chain; at the same time, it provides adsorption sites to further improve the adsorption capacity. Summary of the invention

[0004] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objects of the present invention is to at least solve one or more of the above-mentioned problems in the prior art. In other words, one of the objects of the present invention is to provide a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material and a preparation method and application thereof that meet one or more of the above-mentioned needs.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] A method for preparing a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material comprises the following steps:

[0007] S1, continuously stirring the mixed solution of the cellulose nanocrystal suspension and acrylic acid to form a uniformly dispersed cellulose nanocrystal / acrylic acid mixture;

[0008] S2, adding N,N'-methylenebisacrylamide crosslinking agent to the dispersion obtained in step S1, while continuing continuous magnetic stirring;

[0009] S3, adding nano zero-valent iron to the dispersion obtained in step S2, while continuing to stir magnetically;

[0010] S4, slowly adding ammonium persulfate APS initiator to the dispersion obtained in step S3 until the mixture changes color and forms a semi-solidified colloid;

[0011] S5. Drying the semi-gel mixture obtained in step S4 to obtain a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material.

[0012] As a preferred embodiment, in step S1, the concentration of the cellulose nanocrystal suspension is 1-5 wt %, and the mass ratio of the cellulose nanocrystal to the acrylic acid is 1:(20-100).

[0013] As a preferred solution, in step S1, the rotation speed of the magnetic stirring is 150 to 300 r / min, and the stirring time is 3 to 60 min.

[0014] As a preferred solution, in step S2, the mass of the N,N'-methylenebisacrylamide cross-linking agent is 0.6-1 wt% of the total mass of the cellulose nanocrystals and the acrylic acid.

[0015] As a preferred solution, in step S2, the rotation speed of the magnetic stirring is 150 to 300 r / min, and the stirring time is 3 to 60 min.

[0016] As a preferred solution, in step S3, the mass of nano zero-valent iron is 1-5wt% of the total mass of cellulose nanocrystals and acrylic acid; the speed of magnetic stirring is 150-300 r / min, and the stirring time is 3-60 min.

[0017] As a preferred solution, in step S4, the mass of the ammonium persulfate APS initiator is 0.6-1 wt % of the total mass of the cellulose nanocrystals and the acrylic acid.

[0018] As a preferred solution, in step S5, the drying temperature is 60-120° C. and the drying time is 0.5-2 h.

[0019] The present invention also provides a nano-iron cross-linked cellulose nano-crystal / polyacrylic acid composite material prepared by the preparation method described in any of the above schemes.

[0020] The present invention also provides the use of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material as described in the above scheme for adsorbing diclofenac in wastewater.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material prepared by the present invention has low toxicity, uniformity and biodegradability, and has a large number of adsorption sites, which can efficiently adsorb and remove diclofenac in wastewater;

[0023] (2) The maximum adsorption capacity of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material prepared by the present invention for diclofenac is as high as 730.8 mg / g, and the adsorption conforms to the Langmuir adsorption model, and monolayer adsorption is the main adsorption process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a scanning electron microscope image of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material of Example 1 of the present invention;

[0025] Figure 2 It is a comparison diagram of the adsorption isotherm fitting curves of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material of Example 1 of the present invention and the composite materials of Comparative Examples 1-3 for removing diclofenac;

[0026] Figure 3 This is a data graph of the adsorption capacity of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material of Example 1 of the present invention for removing diclofenac under different pH conditions. DETAILED DESCRIPTION

[0027] The preparation method of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material of the present invention and its preparation method and application are further explained below.

[0028] The preparation method of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material of the present invention specifically comprises the following steps:

[0029] S1, continuously stirring a mixed solution of a cellulose nanocrystal suspension having a concentration of 1 to 5 wt% and acrylic acid to form a uniformly dispersed cellulose nanocrystal / acrylic acid mixture;

[0030] The cellulose nanocrystal suspension is cellulose nanocrystals dispersed in water, and the mass ratio of cellulose nanocrystals to acrylic acid is 1:(20-100); the speed of magnetic stirring is 150-300 r / min, and the stirring time is 3-60 min;

[0031] S2, adding N,N'-methylenebisacrylamide crosslinking agent to the dispersion obtained in step S1, while continuing continuous magnetic stirring;

[0032] The mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.6-1wt% of the total mass of the cellulose nanocrystals and the acrylic acid; the speed of the magnetic stirring is 150-300 r / min, and the stirring time is 3-60 min;

[0033] S3, adding nano zero-valent iron to the dispersion obtained in step S2, while continuing to stir magnetically;

[0034] The mass of the nano-zero-valent iron is 1 to 5 wt% of the total mass of the cellulose nanocrystals and the acrylic acid; the speed of the magnetic stirring is 150 to 300 r / min, and the stirring time is 3 to 60 min;

[0035] S4, slowly adding ammonium persulfate APS initiator to the dispersion obtained in step S3 until the mixture changes color and forms a semi-solidified colloid;

[0036] Wherein, the mass of the ammonium persulfate APS initiator is 0.6-1wt% of the total mass of the cellulose nanocrystals and the acrylic acid;

[0037] S5, heating the semi-gel mixture obtained in step S4 in a forced air drying oven at 60-120° C. for 0.5-2 h to obtain a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material.

[0038] The nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material prepared by the invention has low toxicity, uniformity and biodegradability, and has a large number of adsorption sites, and can efficiently adsorb and remove diclofenac in wastewater.

[0039] The technical solution of the present invention is further explained below through specific embodiments.

[0040] Embodiment 1:

[0041] The preparation method of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material of this embodiment comprises the following steps:

[0042] S1: 100 mL of a mixed solution of a 1 wt % cellulose nanocrystal suspension and acrylic acid (the content of acrylic acid is 3% relative to the mass ratio of the cellulose nanocrystal / acrylic acid mixture) is continuously magnetically stirred to form a uniformly dispersed cellulose nanocrystal / acrylic acid mixture;

[0043] Specifically, the mass ratio of cellulose nanocrystals to acrylic acid was 3:97; the speed of magnetic stirring was 300 r / min, and the stirring time was 10 min;

[0044] S2: adding N,N'-methylenebisacrylamide crosslinking agent to the dispersion obtained in step S1 while continuing to stir magnetically;

[0045] Specifically, the mass of the N,N'-methylenebisacrylamide crosslinking agent is 0.6wt% of the total mass of the cellulose nanocrystals and the acrylic acid, the speed of the magnetic stirring is 300r / min, and the stirring time is 15min;

[0046] S3: adding nano zero-valent iron to the dispersion obtained in step S2 while continuing to stir magnetically;

[0047] Specifically, the mass of nano zero-valent iron is 1wt% of the total mass of cellulose nanocrystals and acrylic acid, the speed of magnetic stirring is 300r / min, and the stirring time is 40min;

[0048] S4: slowly adding the APS initiator to the dispersion obtained in step S3 until the mixture changes color and forms a semi-solidified colloid;

[0049] Specifically, the mass of the APS initiator is 0.6 wt % of the total mass of the cellulose nanocrystals and the acrylic acid;

[0050] S5: The semi-gel mixture obtained in step S4 is heated in a forced air drying oven at 90° C. for 0.5 h to obtain a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material, referred to as Fe@CP.

[0051] like Figure 1As shown, it shows a scanning electron microscope image of the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material prepared in Example 1. It can be seen that the nano-iron cross-linked cellulose nanocrystal / polyacrylic acid hydrogel has a significant porous structure, presenting orderly arranged interconnected pore channels, thin pore walls, and abundant pores. Such a hierarchical porous structure may make it easy for diclofenac to diffuse on the surface of the hydrogel and accumulate at the adsorption site.

[0052] Comparative Example 1:

[0053] The difference between this comparative example and Example 1 is that:

[0054] Step S3 is omitted, that is, nano zero-valent iron is not added, and the remaining steps are the same as those in Example 1 to prepare a cellulose nanocrystal / polyacrylic acid composite material, referred to as CP.

[0055] Comparative Example 2:

[0056] The difference between this comparative example and Example 1 is that:

[0057] The nano zero-valent iron in step S3 of Example 1 is replaced by Fe 3 O 4 Solution, the remaining steps are the same as in Example 1, the prepared Fe 3 O 4 Cross-linked cellulose nanocrystal / polyacrylic acid composite material, referred to as Fe 3 O 4 @CP.

[0058] Comparative Example 3:

[0059] The difference between this comparative example and Example 1 is that:

[0060] The nano zero-valent iron in step S3 of Example 1 is replaced by FeCl 3 The remaining steps are the same as in Example 1. 3+ Cross-linked cellulose nanocrystal / polyacrylic acid composite material, referred to as Fe 3+ @CP.

[0061] The composite materials of Example 1 and Comparative Examples 1-3 were tested for adsorption of diclofenac, as follows:

[0062] 10 mg of the composite materials of Example 1 and Comparative Examples 1-3 were added to 20 mL of 10 mg / L, 20 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 400 mg / L, and 600 mg / L diclofenac solutions, respectively, and the mixture was fully shaken at 200 r / min for 12 h at 25 ° C. The adsorption equilibrium solution was taken and the concentration of diclofenac after adsorption was measured by an ultraviolet spectrophotometer at a wavelength of 276 nm.

[0063] The adsorption isotherm fitting curves of the composite materials of Example 1 and Comparative Examples 1 to 3 for removing diclofenac are as follows: Figure 2 As shown, it can be seen that the Langmuir model fits the adsorption isotherm data well, indicating that monolayer adsorption is the main adsorption process. When the initial diclofenac concentration is low, the adsorption amount of nano-iron cross-linked cellulose nanocrystals / polyacrylic acid composite Fe@CP increases sharply, indicating that there are sufficient adsorption sites on the composite hydrogel. With the increase of the initial concentration of diclofenac, the adsorption trend tends to be stable, indicating that the hydrogel surface tends to be saturated with adsorption. When the initial concentration of diclofenac increases to 600 mg·L -1 The equilibrium adsorption capacity of Fe@CP is 730.8 mg·g -1 , which is higher than that of cellulose nanocrystal / polyacrylic acid composite (CP, 485.0 mg·g -1 ), Fe 3+ Cross-linked cellulose nanocrystals / polyacrylic acid composites (Fe 3+ @CP, 519.5mg g -1 ) and Fe 3 O 4 Cross-linked cellulose nanocrystals / polyacrylic acid composites (Fe 3 O 4 @CP, 490.3mg g -1 ); This is due to the interconnected pore structure and numerous active sites on the Fe@CP surface. -1 ) is also much higher than the other three composite hydrogels. In addition, the adsorption capacity of nano zero-valent iron is only 23.1 mg g -1 .

[0064] Figure 3 The effect of pH value on adsorption capacity. It can be seen that as the pH value increases from 2 to 10, the equilibrium adsorption capacity of Fe@CP decreases by 20.0%; when the pH value increases from 2 to 6, the adsorption capacity remains at 390.0 mg·g -1 When the pH value increased to 8, the adsorption capacity dropped to 358.6 mg·g -1 When the pH value increased to 10, the adsorption capacity dropped to the minimum (317.8 mg g -1 ). The decrease in adsorption capacity can be explained by electrostatic repulsion, because the carboxyl groups on Fe@CP and diclofenac tend to be negatively charged with increasing pH. Overall, Fe@CP maintains a high adsorption capacity in both acidic and neutral environments, and has application prospects in treating acidic wastewater.

[0065] In view of the numerous embodiments of the scheme of the present invention, the raw materials and dosage involved can be selected according to actual needs within the limited range, and the experimental data of each embodiment is huge and numerous, which is not suitable for listing and explaining one by one here, but the content required to be verified and the final conclusion obtained in each embodiment are similar. Therefore, the verification content of each embodiment will not be explained one by one here.

[0066] The above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, according to the ideas provided by the present invention, there will be changes in the specific implementation methods, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material, characterized in that: The following steps are involved: S1, continuously stirring the mixed solution of the cellulose nanocrystal suspension and acrylic acid to form a uniformly dispersed cellulose nanocrystal / acrylic acid mixture; S2, adding N,N'-methylenebisacrylamide crosslinking agent to the dispersion obtained in step S1, while continuing continuous magnetic stirring; S3, adding nano zero-valent iron to the dispersion obtained in step S2, while continuing to stir magnetically; S4, slowly adding ammonium persulfate APS initiator to the dispersion obtained in step S3 until the mixture changes color and forms a semi-solidified colloid; S5. Drying the semi-gel mixture obtained in step S4 to obtain a nano-iron cross-linked cellulose nanocrystal / polyacrylic acid composite material.

2. The preparation method according to claim 1, characterized in that: In the step S1, the concentration of the cellulose nanocrystal suspension is 1-5 wt %, and the mass ratio of the cellulose nanocrystal to the acrylic acid is 1:(20-100).

3. The preparation method according to claim 1, characterized in that: In the step S1, the rotation speed of the magnetic stirring is 150 to 300 r / min, and the stirring time is 3 to 60 min.

4. The preparation method according to claim 1, characterized in that: In the step S2, the mass of the N,N'-methylenebisacrylamide cross-linking agent is 0.6-1 wt% of the total mass of the cellulose nanocrystals and the acrylic acid.

5. The preparation method according to claim 1, characterized in that: In step S2, the rotation speed of the magnetic stirring is 150 to 300 r / min, and the stirring time is 3 to 60 min.

6. The preparation method according to claim 1, characterized in that: In step S3, the mass of nano zero-valent iron is 1-5wt% of the total mass of cellulose nanocrystals and acrylic acid; the speed of magnetic stirring is 150-300 r / min, and the stirring time is 3-60 min.

7. The preparation method according to claim 1, characterized in that: In the step S4, the mass of the ammonium persulfate APS initiator is 0.6-1 wt % of the total mass of the cellulose nanocrystals and the acrylic acid.

8. The method according to claim 1, characterized in that: In step S5, the drying temperature is 60-120° C. and the drying time is 0.5-2 h.

9. The nano-iron cross-linked cellulose nano-crystal / polyacrylic acid composite material obtained by the preparation method according to any one of claims 1 to 8.

10. The use of the nano-iron cross-linked cellulose nano-crystal / polyacrylic acid composite material as claimed in claim 9, characterized in that: Used to adsorb diclofenac in wastewater.

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