CN106517144A - Method for preparing carbon nanofiber aerogel from wood - Google Patents

Abstract

The invention provides a method for preparing carbon nanofiber airgel from wood, comprising: a) pre-treating wood to obtain wood pulp; b) mixing wood pulp with tetramethylpiperidinium oxide, sodium bromide and sodium hypochlorite , carry out an oxidation reaction to obtain a cellulose suspension; c) after the above-mentioned cellulose suspension is suction-filtered, disperse in water, break up to obtain a uniform viscous nano-cellulose solution; d) put the above-mentioned nano-cellulose solution in Under an acidic environment, carry out acidification to obtain nanocellulose hydrogel; e) perform solvent exchange on the above nanocellulose hydrogel in acetone containing p-toluenesulfonic acid, and use _CO2 supercritical drying method to dry to obtain nanocellulose hydrogel Cellulose airgel; f) pyrolyzing the nanocellulose airgel in an inert gas atmosphere of a tube furnace to obtain carbon nanofiber airgel. The invention uses wood as a raw material to prepare carbon nanofiber airgel, which has uniform diameter, low density, large specific surface area, heat insulation and fire resistance, and the like.

Description

A method for preparing carbon nanofiber airgel from wood

technical field

The invention relates to the technical field of nanometer materials, in particular to a method for preparing carbon nanofiber airgel from wood.

Background technique

Carbon nanofiber airgel, which is composed of a three-dimensional network structure, has excellent physical properties such as low density, large specific surface area, high electrical conductivity and porosity, and is a new material that has attracted extensive attention. Carbon aerogels can be used as catalyst supports, artificial muscles, electrodes for supercapacitors, absorbents, and gas detectors. In particular, ultralight or elastic carbon aerogels have many promising applications. For example, ultra-light nitrogen-doped graphene structures are used as absorbers and supercapacitor electrodes, exhibiting a large absorption capacity and special capacitance; elastic conductors based on elastic graphene foams can withstand stretching and bending The electrical conductivity and electrical stability are still maintained.

The prior art discloses a variety of methods for preparing carbon aerogels, such as German "Advanced Materials" (Advanced Materials, 22, 2010, page 617) discloses a dichlorobenzene solution using ferrocene as a precursor, The method of preparing carbon nanotube sponge airgel by chemical vapor deposition method, the carbon nanotube sponge airgel prepared by this method has good mechanical properties, but chemical vapor deposition requires complex and expensive devices, which cannot be used on a large scale production, preventing the prospect of industrial application of the method. German "Applied Chemistry" (AngewandteChemie International Edition, 2012, Issue 51, page 5101) reported that by using glucose as a precursor, a hydrothermal carbonization process was used to prepare carbon fiber aerogels on a large scale, but the process used toxic and expensive Tellurium nanowires are used as templates, and this preparation process is not suitable for commercialization. German "Applied Chemistry" (AngewandteChemie International Edition, 2013, 52, page 2925) reported a method of using bacterial cellulose to prepare ultra-light, elastic and refractory carbon nanofiber airgel, although bacterial cellulose is a typical Biomass materials, but the industrialized fermentation preparation process still requires high costs.

Therefore, in terms of large-scale popularization and application of carbon nanofiber aerogels, it is an urgent problem to find a low-cost preparation method.

Contents of the invention

In view of this, the technical problem to be solved by the present invention is to provide a method for preparing carbon nanofiber airgel from wood, the raw material is wood widely existing in nature, and the preparation cost is very low.

The invention provides a method for preparing carbon nanofiber airgel from wood, comprising:

a) pre-treating wood to obtain wood pulp;

b) mixing the above-mentioned wood pulp with tetramethylpiperidine oxide, sodium bromide and sodium hypochlorite, and performing an oxidation reaction to obtain a cellulose suspension;

c) After the above-mentioned cellulose suspension is suction-filtered, dispersed in water, and dispersed to obtain a uniform viscous nano-cellulose solution;

d) acidifying the nanocellulose solution in an acidic environment to obtain a nanocellulose hydrogel;

e) solvent exchange the above-mentioned nanocellulose hydrogel in acetone containing p-toluenesulfonic acid, and use _CO Supercritical drying method to dry to obtain nanocellulose airgel;

f) Pyrolyzing the nanocellulose airgel in a tube furnace at high temperature to obtain carbon nanofiber airgel.

In the present invention, wood is used as a raw material for the first time to prepare carbon nanofiber airgel. Firstly, ordinary wood is pretreated to obtain wood pulp. Preferably, sodium hydroxide solution and acidic sodium chlorite solution are respectively used to reflux multiple times to obtain bleached wood pulp.

The sodium hydroxide solution is preferably an aqueous sodium hydroxide solution, and its mass concentration is preferably 5wt%-10wt%, more preferably 7wt%.

The acidic sodium chlorite solution is preferably an acidic sodium chlorite aqueous solution, and its mass concentration is preferably 0.5wt%˜1.5wt%, more preferably 1wt%.

The wood pulp is then mixed with tetramethylpiperidinium oxide (TEMPO), sodium bromide and sodium hypochlorite for an oxidation reaction to obtain a cellulose suspension.

Preferably, the mass volume ratio of the solid content of the wood pulp, tetramethylpiperidine oxide, sodium bromide and sodium hypochlorite solution is (1g):(0.01～0.03g):(0.05～0.2g):(5 ～15mL), more preferably (1g):(0.016g):(0.1g):(10ml), the mass content of described sodium hypochlorite solution is preferably 5wt%～15wt%, more preferably 9wt%.

The sodium hypochlorite solution is preferably an aqueous sodium hypochlorite solution.

The temperature of the oxidation reaction is preferably 20°C-25°C, and the time is preferably 4h-10h.

The oxidation reaction is preferably carried out in an alkaline environment, and the pH value of the alkaline environment is preferably 10-103.

Then the cellulose suspension obtained after oxidation is subjected to suction filtration, and the obtained white viscous substance is dispersed in water and dispersed to obtain a uniform viscous nanocellulose solution.

The present application has no special limitation on the dispersing, and it is only necessary to perform a slight mechanical treatment on the cellulose. Preferably, the dispersing uses a stirrer, and the rotation speed is preferably 37,000-50,000 revolutions/min.

Preferably, in the present invention, after breaking up, ultrasonic treatment in a cell disruptor is also included.

Then, the nanocellulose solution is acidified in an acidic environment to obtain a nanocellulose hydrogel.

In the present invention, the acidic compound used in the acidic environment is not particularly limited, and hydrochloric acid is preferably added to the nanocellulose solution for acidification treatment.

The pH value of the acidic environment is preferably 2-3.

Then, the above-mentioned nanocellulose hydrogel was solvent-exchanged in acetone containing p-toluenesulfonic acid, and then dried by _CO2 supercritical drying method to obtain nanocellulose airgel.

Preferably, the mass ratio of the solid content of the nanocellulose hydrogel to p-toluenesulfonic acid is 5-15:1, more preferably 10:1.

The solvent exchange time is 3-4 days.

Preferably, the temperature of the CO ₂ supercritical drying method sample chamber is 50° C., and the pressure is 9.0 MPa.

Finally, the nanocellulose airgel is pyrolyzed in a tube furnace at high temperature to obtain the carbon nanofiber airgel.

The invention utilizes the catalytic dehydration property of p-toluenesulfonic acid to prevent the shrinkage and aggregation of the nano-cellulose airgel during the pyrolysis process, thereby successfully preparing the carbon nano-fiber airgel from wood for the first time.

Preferably in the present invention, the temperature rise program of the high temperature pyrolysis is 2°C/min before 500°C, and 5°C/min after 500°C.

During the temperature rise of the high-temperature pyrolysis, the temperature was kept at 500° C. for 1 h.

The final pyrolysis temperature of the high-temperature pyrolysis is 800° C., and the final temperature is maintained for 1 to 2 hours.

The cooling program of the high-temperature pyrolysis is that the cooling rate is 5°C/min before 500°C, and the temperature is naturally lowered after 500°C.

The protective gas for the high temperature pyrolysis is argon or nitrogen.

Compared with the prior art, the present invention provides a method for preparing carbon nanofiber airgel from wood, comprising: a) pre-treating wood to obtain wood pulp; b) mixing the above wood pulp with tetramethylpiperene Pyroxyl, sodium bromide and sodium hypochlorite are mixed and oxidized to obtain a cellulose suspension; c) After suction filtering the above cellulose suspension, disperse in water and break up to obtain a uniform viscous nano-cellulose solution ; d) acidifying the above-mentioned nanocellulose solution in an acidic environment to obtain a nanocellulose hydrogel; e) performing solvent exchange on the above-mentioned nanocellulose hydrogel in acetone containing p-toluenesulfonic acid, using CO _2. Drying by supercritical drying method to obtain nanocellulose airgel; f) pyrolyzing the nanocellulose airgel in a tube furnace at high temperature to obtain carbon nanofiber airgel.

The present invention realizes for the first time that ordinary wood is used as a raw material to prepare carbon nanofiber airgel materials, and cellulose is stripped by an oxygen-containing free radical reagent (TEMPO) to obtain cellulose nanofibers; The solution forms a hydrogel; then the nanocellulose hydrogel is solvent-substituted with an acetone solution containing p-toluenesulfonic acid and then supercritically dried to obtain a nanocellulose aerogel; the nanocellulose aerogel is inert in a tube furnace The final product carbon nanofiber airgel is obtained by pyrolysis in the gas atmosphere, which provides a new method for preparing carbon nanofiber airgel materials. The diameter of the obtained carbon nanofiber is relatively uniform, ranging from 5 to 10 nm, which is lower than 10 nm. The obtained carbon nanofiber airgel has a low density. The experimental results show that its density is 10-20 mg/cm ³ , and its specific surface area is relatively large. Its BET specific surface area is 703.7389 m2/g, which has good heat insulation and fire resistance. and other characteristics.

In addition, the preparation method of the carbon nanofiber airgel provided by the present invention is simple and easy to implement, and has good repeatability, and the raw material is wood widely existing in nature, so it is very easy to realize large-scale preparation.

Description of drawings

Fig. 1 is the transmission electron micrograph of the nanocellulose that the embodiment of the present invention 1 provides;

Fig. 2 is the atomic force microscope photograph of the nanocellulose provided by Example 1 of the present invention;

Fig. 3 is the digital photograph of the nanocellulose hydrogel that the embodiment of the present invention 1 provides;

Fig. 4 is the scanning electron micrograph of the nanocellulose airgel provided by Example 2 of the present invention;

Fig. 5 is the scanning electron micrograph of the carbon nanofiber airgel provided by Example 2 of the present invention;

Fig. 6 is the digital photograph of the cellulose nanofiber film that the embodiment of the present invention 2 provides;

FIG. 7 is a transmission electron micrograph of carbon nanofibers provided in Example 2 of the present invention.

detailed description

In order to further illustrate the present invention, the method for preparing carbon nanofiber airgel from wood provided by the present invention will be described in detail below in conjunction with examples.

Each raw material in each of the following examples is purchased from the market.

Example 1

Disperse 3.75g of bleached wood pulp (solid content 26.67%) into 100mL of water, stir well, then add 0.016g, 0.1mmol tetramethylpiperidine oxide and 0.1g, 1mmol sodium bromide, use 1M hydrochloric acid Adjust 10ml of 9% sodium hypochlorite solution to a pH of 10, add the sodium hypochlorite solution with a pH of 10 into the dispersion, keep stirring, use a pH meter to detect the pH change of the solution, and add 1M sodium hydroxide dropwise during the reaction to keep the pH of the solution After reacting for 4 to 10 hours, filter with suction, wash with deionized water several times, and disperse the white viscous substance after suction filtration in 100ml of water. The obtained dispersion liquid was mechanically processed in a mixer at a speed of about 37000/min, and after stirring, it was ultrasonically treated in a cell disruptor to obtain a nanocellulose solution.

Add dropwise 1M hydrochloric acid to 20mL of 0.6wt% nanocellulose solution until the pH is 2, place the nanocellulose hydrogel formed at this time in dilute hydrochloric acid solution for 12h to obtain a firm nanocellulose hydrogel . Thereafter, the nanocellulose hydrogel was placed in an acetone solution containing p-toluenesulfonic acid for solvent replacement, keeping the mass ratio of cellulose solid content to p-toluenesulfonic acid at 10:1, and the solvent was replaced twice in 24 hours. The replacement time is 3 to 4 days. The nanocellulose gel after the replacement of the solvent is subjected to carbon dioxide supercritical drying to obtain the nanocellulose airgel, and the parameters of the supercritical drying are set at 50° C. and 9.0 MPa.

The obtained nanocellulose airgel was pyrolyzed in a tube furnace at a high temperature. The heating process was to raise the temperature to 500°C at a rate of 2°C/min, keep it for 1 hour, and then raise the temperature to 800°C at a rate of 5°C/min. , after keeping for 1h, cool down to 500°C at a rate of 5°C/min, and cool down to room temperature naturally after 500°C. Nitrogen is used as the atmosphere gas for pyrolysis throughout the process. Finally, carbon nanofiber airgel is obtained.

The nanocellulose solution was observed with a transmission electron microscope, and the results are shown in FIG. 1 . It can be seen from Figure 1 that the nanocellulose prepared in Example 1 has been fully exfoliated and well dispersed in the aqueous solution. The lower left figure is a digital photo of the nanocellulose solution prepared in Example 1.

The nanocellulose solution was observed with an atomic force microscope, and the results are shown in FIG. 2 . It can be seen from Figure 2 that the nanocellulose prepared in Example 1 has been fully exfoliated and well dispersed in the aqueous solution, and the results in Figure 2 and Figure 1 are mutually confirmed.

Fig. 3 shows the strong cellulose nanofiber hydrogel. It can be seen from Fig. 3 that the cellulose nanofiber hydrogel prepared in Example 1 is translucent.

Example 2

Disperse 3.75g of bleached wood pulp (solid content 26.67%) into 100mL of water, stir well, then add 0.016g, 0.1mmol tetramethylpiperidine oxide and 0.1g, 1mmol sodium bromide, use 1M hydrochloric acid Adjust 10ml of 9% sodium hypochlorite solution to a pH of 10, add the sodium hypochlorite solution with a pH of 10 into the dispersion, keep stirring, use a pH meter to detect the pH change of the solution, and add 1M sodium hydroxide dropwise during the reaction to keep the solution The pH is 10-10.3. After reacting for 4-10 hours, filter with suction, wash with deionized water several times, and disperse the white viscous substance after suction filtration in 100ml of water. The obtained dispersion liquid was mechanically processed in a mixer at a speed of about 37000/min, and after stirring, it was ultrasonically treated in a cell disruptor to obtain a nanocellulose solution.

Take 10ml of the 0.4wt% nanocellulose solution to cover the bottom of a glass petri dish about 7 cm up to now, and place the glass petri dish in an oven at 80° C. for 1 to 2 hours to obtain a nanocellulose transparent film.

Add dropwise 1M hydrochloric acid to 20mL of 0.6wt% nanocellulose solution until the pH is 2, place the nanocellulose hydrogel formed at this time in dilute hydrochloric acid solution for 12h to obtain a firm nanocellulose hydrogel . Thereafter, the nanocellulose hydrogel was placed in an acetone solution containing p-toluenesulfonic acid for solvent replacement, keeping the mass ratio of cellulose solid content to p-toluenesulfonic acid at 10:1, and the solvent was replaced twice in 24 hours. The replacement time is 3 to 4 days. The nanocellulose gel after the replacement of the solvent is subjected to carbon dioxide supercritical drying to obtain the nanocellulose airgel, and the parameters of the supercritical drying are set at 50° C. and 9.0 MPa.

The obtained nanocellulose airgel was pyrolyzed in a tube furnace at a high temperature. The heating process was to raise the temperature to 500°C at a rate of 2°C/min, keep it for 1 hour, and then raise the temperature to 800°C at a rate of 5°C/min. , after keeping for 1h, cool down to 500°C at a rate of 5°C/min, and cool down to room temperature naturally after 500°C. Nitrogen is used as the atmosphere gas for pyrolysis throughout the process. Finally, carbon nanofiber airgel is obtained.

Take a small amount of the above-mentioned carbon nanofiber airgel in a 5ml centrifuge tube, add 4ml of ethanol solution, and perform ultrasonic treatment for 1-2 hours to obtain a black carbon nanofiber ethanol dispersion, which is used to prepare samples for transmission electron microscopy characterization.

The field emission scanning electron microscope observation is carried out to described nanocellulose aerogel, see Fig. 4 for the result, Fig. 4 is the scanning electron micrograph of the nanocellulose aerogel provided in the embodiment 2 of the present invention, as can be seen from Fig. 4, the present invention The obtained nanofiber airgel has a relatively uniform diameter of about 5 nm. The bottom left figure is a digital photo of the nanocellulose airgel.

The carbon nanofiber aerogel is observed by a field emission scanning electron microscope, and the results are shown in Figure 5. Figure 5 is a scanning electron micrograph of the carbon nanofiber aerogel provided in Example 2 of the present invention. As can be seen from Figure 5, the present invention The obtained carbon nanofiber airgel has a relatively uniform diameter of about 5 nm. The bottom left figure is a digital photo of carbon nanofiber airgel. Comparing Figure 5 with Figure 4, it can be seen that before and after the pyrolysis process, the nanofibers in the airgel did not aggregate, and still maintained the original nanofiber airgel state.

Fig. 6 is a digital photo of the nanocellulose transparent film provided in Example 2 of the present invention. It can be seen from Fig. 6 that the nanocellulose film prepared in Example 2 of the present invention has high transparency.

Carry out transmission electron microscope observation to described carbon nanofiber ethanol dispersion liquid sample, see Fig. 7 for the result, Fig. 7 is the transmission electron microscope photo of the carbon nanofiber ethanol dispersion liquid sample provided in the embodiment 2 of the present invention, can know this by Fig. 7 The carbon nanofibers prepared by the invention are not aggregated with each other, and the diameter distribution is uniform, which is about 5nm. The lower left figure is a digital photo of carbon nanofiber ethanol dispersion.

It can be known from the above examples that the present invention uses wood as a raw material to successfully prepare carbon nanofiber airgel.

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (10)

1. a method for preparing carbon nanofiber airgel by wood, is characterized in that, comprises: a) pre-treating wood to obtain wood pulp; b) mixing the above-mentioned wood pulp with tetramethylpiperidine oxide, sodium bromide and sodium hypochlorite, and performing an oxidation reaction to obtain a cellulose suspension; c) After the above-mentioned cellulose suspension is suction-filtered, dispersed in water, and dispersed to obtain a uniform viscous nano-cellulose solution; d) acidifying the nanocellulose solution in an acidic environment to obtain a nanocellulose hydrogel; e) solvent exchange the above-mentioned nanocellulose hydrogel in acetone containing p-toluenesulfonic acid, and use _CO Supercritical drying method to dry to obtain nanocellulose airgel; f) Pyrolyzing the nanocellulose airgel in a tube furnace at high temperature to obtain carbon nanofiber airgel. 2. preparation method according to claim 1, is characterized in that, the pretreatment of described step a) is specifically: The sodium hydroxide solution and the acidic sodium chlorite solution were refluxed several times. 3. preparation method according to claim 1, is characterized in that, the mass volume ratio of the solid content of described wood pulp, tetramethyl piperidine oxide, sodium bromide and sodium hypochlorite solution is (1g): (0.01～ 0.03g): (0.05～0.2g): (5～15mL), the mass content of the sodium hypochlorite solution is 5wt%～15wt%. 4. The preparation method according to claim 1, characterized in that, the dispersing is performed by using a mixer with a rotating speed of 37000-50000 rpm. 5. The preparation method according to claim 1, characterized in that, the pH value of the acidic environment is 2-3. 6. The preparation method according to claim 1, characterized in that, the mass ratio of the solid content of the nanocellulose hydrogel to p-toluenesulfonic acid is 5 to 15:1. 7. The preparation method according to claim 1, characterized in that, the temperature of the _CO2 supercritical drying method sample chamber is 40°C to 50°C, and the pressure is 9.0MPa. 8. The preparation method according to claim 1, wherein the heating program of the high-temperature pyrolysis is 2°C/min before 500°C, and 5°C/min after 500°C; the high-temperature pyrolysis The cooling program is that the cooling rate is 5 °C/min before 500 °C, and the cooling rate is natural after 500 °C. 9. The preparation method according to claim 1, characterized in that, during the temperature rise of the high-temperature pyrolysis, the temperature is maintained at 500° C. for 1 h. 10. The preparation method according to claim 1, characterized in that, the final pyrolysis temperature of the high temperature pyrolysis is 800°C-1200°C, and the final temperature is maintained for 2 hours.