阅读说明：本技术 一种功能化纤维素纳米纤维气凝胶及其制备方法 (Functionalized cellulose nanofiber aerogel and preparation method thereof ) 是由 周栋梁 秦玉娇 赵君 于 2019-09-20 设计创作，主要内容包括：本发明公开了一种功能化纤维素纳米纤维气凝胶及其制备方法。本发明所述功能化纤维素纳米纤维气凝胶通过采用醛基改性纤维素纳米纤维和接枝酰肼基团的纤维素纳米纤维之间发生化学反应引入腙键的方法制得。本发明所述纤维素纳米纤维气凝胶具有良好的机械稳定性和形状恢复性。(The invention discloses a functionalized cellulose nanofiber aerogel and a preparation method thereof. The functionalized cellulose nanofiber aerogel is prepared by adopting a method of introducing a hydrazone bond through chemical reaction between aldehyde group modified cellulose nanofiber and cellulose nanofiber grafted with a hydrazide group. The cellulose nanofiber aerogel disclosed by the invention has good mechanical stability and shape recovery.)

1. The functionalized cellulose nanofiber aerogel is characterized by being prepared by adopting a method of introducing a hydrazone bond through chemical reaction between aldehyde-group modified cellulose nanofibers and cellulose nanofibers grafted with hydrazide groups;

the mass ratio of the aldehyde group modified cellulose nano-fiber to the cellulose nano-fiber grafted with the hydrazide group is 1: 1.

2. the preparation method of the functionalized cellulose nanofiber aerogel as claimed in claim 1, which is characterized by comprising the following steps:

(1) preparation of hydrazide group functionalized cellulose nanofiber: dispersing 5g of crushed filter paper in 500mL of deionized water, adding 0.06g of TEMPO and 1.0g of NaBr, then dropwise adding 30mL of sodium hypochlorite aqueous solution, adjusting the pH value to be within the range of 10.0-11.0 by using sodium hydroxide solution in the dropwise adding process until the pH value is not changed any more, reacting the mixture for 24 hours, and then centrifuging and dialyzing the product; carrying out ultrasonic treatment on the cellulose nanofiber dispersion system after dialysis for 30min under the power of 300W to obtain uniformly dispersed cellulose nanofiber suspension; grafting 3, 3' -dithio-dipropionic acid dihydrazide with free hydrazide groups on the cellulose nanofibers through hydrazide reaction to prepare hydrazide functionalized cellulose nanofibers;

(2) preparing cellulose nano-fibers with aldehyde groups: 1.5g of NaIO₄Dissolving the mixture in 200mL of 1wt% cellulose nanofiber suspension, stirring the mixture in a dark environment for 2 hours, and dialyzing the obtained product to obtain cellulose nanofibers with aldehyde groups;

(3) preparing a functionalized cellulose nanofiber aerogel: mixing two different modified cellulose nanofiber suspensions prepared in the steps (1) and (2) according to the mass ratio of 1: 1, mixing, magnetically stirring for 5-10 min to uniformly mix, stopping stirring, standing to form hydrogel, wherein the time for forming the hydrogel is different according to different concentrations of suspension; thereafter, the hydrogel was left to stand at room temperature for 5h to age it; and (2) putting the cellulose nanofiber hydrogel into an absolute ethanol solution, performing solvent replacement at room temperature, and freeze-drying the cellulose nanofiber hydrogel subjected to sufficient solvent replacement to obtain the functionalized cellulose nanofiber aerogel disclosed by the invention.

3. The method for preparing the functionalized cellulose nanofiber aerogel according to claim 2, wherein the method for preparing the cellulose nanofiber suspension in the step (2) comprises the following steps: and hydrolyzing filter paper by adopting 64wt% of sulfuric acid, controlling the reaction temperature and the reaction time to ensure that the non-crystallization area of the cellulose is hydrolyzed and the crystallization area is not damaged, and centrifuging and dialyzing the paper pulp after the reaction is finished until the pH value is not changed any more to obtain the cellulose nanofiber suspension.

Technical Field

The invention relates to the field of aerogels, in particular to a functionalized cellulose nanofiber aerogel and a preparation method thereof.

Background

With the increasing severity of environmental pollution, energy crisis and other problems, Cellulose Nanofibers (CNFs) of natural biological origin have attracted more and more attention due to their abundant reserves, renewability and good biodegradability. The CNFs aerogel prepared by taking the CNFs as the raw material has low toxicity, biodegradability, good biocompatibility and unique pore structure, and has wide application prospect in the fields of electrochemistry, biomedicine, architecture and the like. In addition, the CNFs surface has a large amount of active hydroxyl groups, and chemical modification is easy to realize, so that more application prospects are provided for the practical application research of CNFs aerogel, including sewage purification materials, magnetic materials, catalyst loading materials and the like. It is worth noting that most of the applications relating to CNFs aerogels need to be carried out in an environment in which water is present. However, in a water environment, water molecules and hydroxyl groups on the CNFs can form hydrogen bonds, so that the hydrogen bonds between the cellulose are replaced by the hydrogen bonds between the cellulose and the water molecules, and therefore, the CNFs aerogel is very easy to decompose and damage in the application process, so that the CNFs material is poor in water resistance and poor in recyclability.

CNFs aerogel with SiO₂Aerogel has similar characteristics of higher porosity and larger specific surface area, but compared with SiO₂Aerogels, CNFs aerogels, have certain compressive properties and are not brittle, and therefore can be suitable for applications requiring flexibility and certain mechanical strength. However, the application of CNFs aerogel has a certain limitation, that is, CNFs aerogel has a tendency to decompose in water, which is mainly because water molecules can form hydrogen bonds with hydroxyl groups on cellulose nanofibers, and the basic structure of the aerogel is destroyed in water environment. To overcome this deficiency of CNFs aerogels, three solutions have been proposed: (1) introducing a polymer into the CNFs suspension to form a stable composite aerogel; (2) adding a cross-linking agent into the CNFs suspension to increase the cross-linking between the CNFs and form stable CNFs aerogel; (3) chemical crosslinking is introduced into the CNFs to replace partial hydrogen bond crosslinking, so that the mechanical property of the CNFs aerogel is enhanced. Since the first scheme and the second scheme inevitably cover part of the hydrophilic sites on the surface of the cellulose nanofibers, the third scheme becomes the best scheme for improving the water resistance of the CNFs aerogel.

Yang et al introduced chemical crosslinking in Cellulose Nanocrystalline (CNC) aerogel, prepared the cellulose aerogel with certain water resistance, and this aerogel still reached 85% shape recovery rate after cyclic compression 20 times under 80% compression capacity in water environment. However, the cellulose nanocrystals have a small aspect ratio, high hardness and poor flexibility, so that the physical entanglement is relatively weak, and the cellulose nanocrystals have many defects in the process of forming cellulose aerogels, and are not the best material for forming cellulose aerogels.

Li et al introduce ester crosslinking in CNFs aerogel through efficient gas-solid fluorination reaction, achieve the goal of coexistence of covalent bond and hydrophilic group in CNFs aerogel, and improve the mechanical properties and water resistance of CNFs aerogel. After chemical treatment, the pore diameter of the aerogel is increased from 3.1nm to 5.6nm, the pore diameter is mainly increased because the bond path of a covalent bond is shorter than that of a hydrogen bond, the distance between CNFs is reduced, and the pore diameter is increased. However, fluorine gas is a strong oxidant, has strong corrosivity and strong toxicity, and is easy to cause harm to the environment and human bodies, so the fluorine gas oxidation method is not a common oxidation method.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a functionalized cellulose nanofiber aerogel and a preparation method thereof, which can improve the mechanical stability and water resistance of the CNFs aerogel and ensure the hydrophilicity of the CNFs aerogel at the same time by a proper method.

According to the invention, the cellulose nanofiber aerogel with good mechanical stability and shape recovery is prepared by adopting a method of introducing a hydrazone bond through chemical reaction between aldehyde group modified cellulose nanofiber and cellulose nanofiber grafted with a hydrazide group; the mass ratio of the aldehyde group modified cellulose nano-fiber to the cellulose nano-fiber grafted with the hydrazide group is 1: 1.

the invention relates to a preparation method of a functionalized cellulose nanofiber aerogel, which specifically comprises the following steps:

(1) preparation of hydrazide group functionalized cellulose nanofiber: dispersing 5g of crushed filter paper in 500mL of deionized water, adding 0.06g of TEMPO and 1.0g of NaBr, then dropwise adding 30mL of sodium hypochlorite aqueous solution, adjusting the pH value to be within the range of 10.0-11.0 by using sodium hydroxide solution in the dropwise adding process until the pH value is not changed any more, reacting the mixture for 24 hours, and then centrifuging and dialyzing the product; carrying out ultrasonic treatment on the cellulose nanofiber dispersion system after dialysis for 30min under the power of 300W to obtain uniformly dispersed cellulose nanofiber suspension; grafting 3, 3' -dithio-dipropionic acid dihydrazide with free hydrazide groups on the cellulose nanofibers through hydrazide reaction to prepare hydrazide functionalized cellulose nanofibers;

the invention selects 3, 3' -dithio-dihydrazide as a functional group to realize the crosslinking of the cellulose nano-fiber aerogel mainly due to two reasons: (1) after the 3, 3' -dithio-dihydrazide reacts with carboxyl, a free hydrazide group exists on the surface of the cellulose, so that the possibility is provided for the subsequent reaction; (2) the 3, 3' -dithio-dihydrazide molecule contains disulfide bond and hydrazide group, which provides possible adsorption site for the subsequent adsorption of titanium precursor on the surface of aerogel.

(2) Preparing cellulose nano-fibers with aldehyde groups: 1.5g of NaIO₄Dissolving in 200mL of 1wt% cellulose nanofiber suspension, stirring the mixture in a dark environment for 2 hours, and dialyzing the obtained product to obtain cellulose nanofibers with aldehyde groups;

(3) preparing a functionalized cellulose nanofiber aerogel: mixing two different modified cellulose nanofiber suspensions prepared in the steps (1) and (2) according to the mass ratio of 1: 1, mixing, magnetically stirring for 5-10 min to uniformly mix, stopping stirring, standing to form hydrogel, wherein the time for forming the hydrogel is different according to different concentrations of suspension; thereafter, the hydrogel was left to stand at room temperature for 5h to age it; and (2) putting the cellulose nanofiber hydrogel into an absolute ethanol solution, performing solvent replacement at room temperature, and freeze-drying the cellulose nanofiber hydrogel subjected to sufficient solvent replacement to obtain the functionalized cellulose nanofiber aerogel disclosed by the invention.

The preparation method of the cellulose nanofiber suspension in the step (2) comprises the following steps: and hydrolyzing filter paper by adopting 64wt% of sulfuric acid, controlling the reaction temperature and the reaction time to ensure that the non-crystallization area of the cellulose is hydrolyzed and the crystallization area is not damaged, and centrifuging and dialyzing the paper pulp after the reaction is finished until the pH value is not changed any more to obtain the cellulose nanofiber suspension.

In order to overcome the problems of poor mechanical property and easy dispersion in water environment of cellulose nanofiber aerogel, the invention introduces chemical crosslinking into the cellulose nanofiber aerogel, and generates hydrazone bonds mainly through the reaction of hydrazide groups on the cellulose nanofiber functionalized by hydrazide groups and aldehyde groups on the cellulose nanofiber with aldehyde groups.

The functionalized cellulose nanofiber aerogel prepared by the method is in a macroporous and mesoporous coexisting hierarchical pore structure, and has good mechanical properties and shape recovery performance in a water environment; and the functionalized cellulose nanofiber aerogel has larger adsorption capacity to RhB organic pollutants due to the characteristics of unique pore structure, larger specific surface area, surface negative charge and the like.

Detailed Description

The present invention will be described in detail with reference to specific examples.

A preparation method of a functionalized cellulose nanofiber aerogel specifically comprises the following steps:

(1) preparation of hydrazide group functionalized cellulose nanofiber: dispersing 5g of crushed filter paper in 500mL of deionized water, adding 0.06g of TEMPO and 1.0g of NaBr, then dropwise adding 30mL of sodium hypochlorite aqueous solution, adjusting the pH value to be within the range of 10.0-11.0 by using sodium hydroxide solution in the dropwise adding process until the pH value is not changed any more, reacting the mixture for 24 hours, and then centrifuging and dialyzing the product; carrying out ultrasonic treatment on the cellulose nanofiber dispersion system after dialysis for 30min under the power of 300W to obtain uniformly dispersed cellulose nanofiber suspension; grafting 3, 3' -dithio-dipropionic acid dihydrazide with free hydrazide groups on the cellulose nanofibers through hydrazide reaction to prepare hydrazide functionalized cellulose nanofibers;

(2) preparing cellulose nano-fibers with aldehyde groups: 1.5g of NaIO₄Dissolving in 200mL of 1wt% cellulose nanofiber suspension, stirring the mixture in a dark environment for 2 hours, and dialyzing the obtained product to obtain cellulose nanofibers with aldehyde groups;

(3) preparing a functionalized cellulose nanofiber aerogel: mixing two different modified cellulose nanofiber suspensions prepared in the steps (1) and (2) according to the mass ratio of 1: 1, mixing, magnetically stirring for 5-10 min to uniformly mix, stopping stirring, standing to form hydrogel, wherein the time for forming the hydrogel is different according to different concentrations of suspension; thereafter, the hydrogel was left to stand at room temperature for 5h to age it; and (2) putting the cellulose nanofiber hydrogel into an absolute ethanol solution, performing solvent replacement at room temperature, and freeze-drying the cellulose nanofiber hydrogel subjected to sufficient solvent replacement to obtain the functionalized cellulose nanofiber aerogel disclosed by the invention.