CN105689012B - A kind of preparation method of Nano diamond solid acid catalyst - Google Patents

Abstract

A method for preparing a nano-diamond solid acid catalyst, the specific steps are as follows: using radio-frequency plasma radio-frequency technology to carry out amino terminal modification on nano-diamond powder. Then, choose zirconium oxide particles as the auxiliary medium, and use ultrasonic dispersion technology to obtain a stable dispersion of nano-diamonds in THF or dimethylformamide solvents. Finally, the amino terminal on the surface of the nano-diamond reacts with 1,3-sultone to prepare sulfonic acid sites on the nano-diamond, which is centrifugally cleaned and dried with deionized water to obtain the final product of the nano-diamond solid acid catalyst. The invention proposes a preparation method of a novel nano-diamond solid acid catalyst based on the surface amino terminal modification and sulfonation reaction of the nano-diamond particles. Compared with the existing methods for preparing nano-diamonds based on hydroxyl terminals, the preparation method of the present invention has outstanding advantages such as significantly shortened reaction time, simple and easy process flow, and the like.

Description

A kind of preparation method of nano diamond solid acid catalyst

technical field

The invention belongs to the field of nano functional materials, in particular to a preparation method of a nano diamond solid acid catalyst.

Background technique

Solid acid catalysts are an important class of catalysts. Its catalytic function comes from the catalytically active acidic sites on the surface of solid materials, called acid centers. This kind of catalyst is widely used in the fields of alkaline sewage treatment, ester compound synthesis, fuel cell ion conductor and so on. Compared with traditional liquid acids, solid acids have outstanding advantages such as high acid strength, low corrosion and easy separation in catalytic systems. At present, solid acid catalyst materials are mostly non-transition element oxides and elemental carbon particles. Among them, nanomaterials are considered to be ideal matrix materials for solid acid catalysts because of their high specific surface area, strong hydrophobicity, and good adsorption compatibility with organic matter. However, under some special conditions of use, ordinary nanopowders have poor chemical stability due to their high surface energy, making them unsuitable for use as matrix materials for solid acid catalysts. For example, when manufacturing ionic conductors in fuel cells, the solid acid catalyst used needs to maintain dimensional stability and acid catalytic activity for a long time under high temperature conditions to ensure the service life of the fuel cell. Under such conditions, traditional nano-oxide solid acid catalysts are difficult to meet the requirements of use, while nano-diamond solid catalysts are considered to be ideal for this type of solid catalyst substrate because of their advantages in thermal stability, high mechanical strength and stable chemical properties. choose.

Due to the high chemical stability of diamond itself, to obtain acid centers on its surface, it must be chemically modified first. There is only one method for preparing nano-diamond solid acid catalysts that has been reported so far. The specific steps are: first, use hydrogen peroxide to purify the nano-diamonds with hydroxyl groups on the surface, then wash them with deionized water, isopropanol and acetone in sequence, and then disperse them in the 1,3-endesulphonate/toluene system, Stir and react at 100°C for a certain period of time (usually 24h) to obtain a solid acid catalyst with sulfonic acid sites on the surface. From the perspective of practical application effect, there are two main problems in the above preparation method. First, due to the high surface energy of nano-diamonds, long-term high-temperature reaction will easily lead to agglomeration of nanoparticles, and subsequent secondary dispersion is difficult, thus affecting catalytic activity. . Second, the above-mentioned method has a long reaction time and a high temperature, and a toluene condensation reflux device needs to be provided in the reaction process. The equipment is complicated and the energy consumption is high, which is unfavorable for large-scale production. For this reason, the present invention proposes a novel nano-diamond solid acid catalyst preparation method based on ultrasonic dispersion technology.

Contents of the invention

The present application uses zirconia-assisted ultrasonic dispersion technology to overcome the agglomeration problem in the existing nano-diamond solid acid catalyst preparation technology. Compared with the traditional method, the shortening of the reaction time and the reduction of the temperature are also helpful to overcome the agglomeration and realize the large-scale production of this type of catalyst. This application uses nano-diamonds with amino terminals to quickly prepare a A novel nano-diamond solid acid catalyst. Compared with the existing method, the method has the outstanding advantages of short reaction time, difficulty in agglomeration of nanoparticles and the like.

In order to achieve the above object, the technical scheme adopted by the application is as follows:

A kind of nano diamond solid acid catalyst, its structural formula is as follows:

When the catalyst is in an alkaline environment, in the molecular structure of the catalyst, the H ⁺ combined with the acid center will undergo an ion exchange reaction with the metal cation of the strong acid salt that causes pollution, so that the pH value in the solution is reduced, and the nanodiamond Agglomeration and sedimentation occur when the colloidal stability is lost in the liquid dispersion system. At this time, the sediment can be recovered for the second time and reused, which solves the problem that the traditional liquid acid cannot be separated.

The method for preparing a nano-diamond solid acid catalyst, the specific steps are as follows:

(1) carry out amino terminal modification to nano-diamond powder;

(2) purifying and dispersing the nano-diamond powder modified by the amino terminal obtained in step (1);

(3) performing sulfonation treatment on the product treated in step (2) to obtain a nano-diamond solid acid catalyst.

Described, in step (1), the concrete steps of carrying out amino terminal modification to nano-diamond powder are as follows:

Single-crystal nano-diamonds with an average particle size of less than 100nm were ultrasonically cleaned with deionized water, ammonia water, and ethanol for 10 minutes, and then placed in the vacuum chamber of the low-pressure plasma processing equipment, and vacuumed to below 10Pa; then according to the flow ratio 2:1 simultaneously inject hydrogen and nitrogen, and finally apply radio frequency electricity to the gas in the vacuum chamber to obtain plasma, take out the sample after processing for 5-20 minutes, and obtain nano-diamond powder with amino terminal on the surface, referred to as ND.

The plasma discharge power is 100w;

Under the action of high-frequency electricity, nitrogen and hydrogen are ionized into active charged nitrogen and hydrogen ions, and at the same time, the CH bonds on the ND surface are opened, thereby re-forming the C- _NH2 structure on the ND surface.

In the described step (2), the specific steps of purifying and dispersing the nano-diamond powder modified by the amino terminal are as follows:

Weigh zirconia powder (ZrO ₂ ) according to 100-200 times the weight of ND, place ZrO ₂ at the bottom of the container, spread ND evenly on it, and then add tetrahydrofuran (THF) or dimethylformamide ( DMF), the container was placed in an ultrasonic processor for 2 hours, and centrifuged to remove ZrO ₂ to obtain ND dispersion;

The amount of tetrahydrofuran (THF) or dimethylformamide (DMF) is 5-10 times the volume of all solids.

The nano-diamond powder exists in the form of nano-diamond aggregates. To remake it into nanoparticles, the first step is to disperse it in a highly polar THF or DMF solvent through ultrasonic vibration; during this process _The ZrO2 in the medium will continuously hit the surface of the diamond grains to remove the defects and impurities of the ND crystal.

The specific steps of the sulfonation treatment are as follows: add 1,3-sultone (PS) 2 times the weight of ND to the ND dispersion, and after ultrasonic treatment at room temperature for 6-8 hours, use deionized water to centrifugally wash three times Afterwards, the precipitate was dried to obtain the final product. The reaction principle is shown in Figure 1.

Compared with the existing methods for preparing nano-diamonds based on hydroxyl terminals, the preparation method of the present invention has outstanding advantages such as significantly shortened reaction time, simple and easy process flow, and the like. Specifically: 1. The introduction of ZrO ₂ particle-assisted ultrasonic dispersion and the entire reaction process are carried out under ultrasonic conditions, effectively avoiding the agglomeration of nanoparticles; 2. The biggest difference is based on the amino terminal connection of sulfonic acid. The previous ones were all terminated with hydroxyl groups. Under the condition of toluene evaporation and reflux, the reaction took more than 24 hours. The equipment and process were complicated. The temperature was above 110 degrees Celsius, and secondary agglomeration easily occurred. But the reaction time of the present invention is 6-8 hours, and effect is good.

ND is the abbreviation of nano-diamond powder with amino terminal modification on the surface;

Description of drawings

Fig. 1 is the schematic diagram of the nano-diamond sulfonation reaction modified with an amino terminal;

Fig. 2 is the FTIR spectral line of the ND diamond solid acid catalyst described in Example 2.

detailed description

Example 1

A kind of preparation method of nano diamond solid acid catalyst, concrete steps are as follows:

(1) Carry out amino terminal modification to the nano-diamond powder. Select single-crystal nano-diamonds with an average particle size of 20-30nm, and perform ultrasonic cleaning with deionized water, ammonia water, and ethanol for 10 minutes, and then place them in the vacuum chamber of the low-pressure plasma processing equipment, and evacuate to 2Pa. Subsequently, hydrogen gas and nitrogen gas (both with a purity of 99.99%) were introduced into the vacuum chamber at a flow rate of 0.5 L/min and 1 L/min. Finally, a rectangular wave radio frequency with a frequency of 10 MHz is applied between the electrodes in the vacuum chamber and the outer shell of the vacuum chamber to obtain plasma. After the plasma glow is stable, stabilize it for 15 minutes, turn off the RF power supply and gas in turn, open the vacuum chamber, and take out the ND.

(2) Purification and dispersion of nanodiamonds. Weigh 40g of _ND200mg ZrO2 with an average particle size of 0.05mm, place ZrO2 at the bottom of the container, spread ND evenly _on it, and then add 20mLTHF. Subsequently, the container containing the above samples was placed in an ice bath, the ultrasonic horn of the ultrasonic processor was inserted into the bottom of the container, the continuous pulse mode was selected, and the frequency of 20KHz was processed for 2 hours. Finally, centrifuge at 5000rpm for 5min, retain the previous supernatant, and wash the lower layer of ZrO ₂ sediment by centrifugation twice with a small amount of THF. The supernatant and the supernatant obtained by the first centrifugation are combined to form the ND dispersion.

(3) Nano-diamond sulfonation treatment. 400mgPS was added to the ND dispersion, after ultrasonic treatment at room temperature (the conditions were the same as the previous step) for 6 hours, after centrifugation and washing with deionized water three times, the precipitate was dried to obtain the final product.

(4) FTIR detection results showed that there were characteristic absorption peaks of functional groups such as C=C, -OH and -SO ₃ H in the sample, indicating that the sulfonation treatment was successful. The average particle size of the product in water measured by a laser particle size analyzer was 83.2±0.5 nm, and the Zeta potential was 30.3 mV.

Example 2

A kind of preparation method of nano diamond solid acid catalyst, concrete steps are as follows:

(1) Carry out amino terminal modification to the nano-diamond powder. Single-crystal nano-diamonds with an average particle size of 60-80nm were ultrasonically cleaned with deionized water, ammonia water, and ethanol for 10 minutes in sequence, and then placed in a vacuum chamber of a low-pressure plasma processing equipment and evacuated to 1Pa. Subsequently, hydrogen gas and nitrogen gas (both with a purity of 99.99%) were fed into the vacuum chamber at flow rates of 1 L/min and 2 L/min. Finally, a rectangular wave radio frequency with a frequency of 15 MHz is applied between the electrodes in the vacuum chamber and the outer shell of the vacuum chamber to obtain plasma. After the plasma glow stabilizes for 9 minutes, turn off the radio frequency power supply and gas in turn, open the vacuum chamber, and take out the ND.

(2) Purification and dispersion of nanodiamonds. Weigh 40 g of ZrO ₂ with ND 200 mg and an average particle size of 0.05 mm, place ZrO ₂ at the bottom of the container, spread ND evenly on it, and then add 30 mL of DMF. Subsequently, the container containing the above samples was placed in an ice bath, the ultrasonic horn of the ultrasonic processor was inserted into the bottom of the container, the continuous pulse mode was selected, and the frequency of 20KHz was processed for 2 hours. Finally, centrifuge at 5000rpm for 5min, retain the previous supernatant, and wash the lower layer of ZrO ₂ sediment by centrifugation twice with a small amount of THF. The supernatant and the supernatant obtained by the first centrifugation are combined to form the ND dispersion.

(3) Nano-diamond sulfonation treatment. 400mgPS was added to the ND dispersion, after 8 hours of sonication at room temperature (conditions as in the previous step), centrifugation with deionized water was used to wash three times, and the precipitate was dried to obtain the final product.

(4) FTIR detection results showed that there were characteristic absorption peaks of functional groups such as C=O, -OH and -SO ₃ H in the sample, indicating that the sulfonation treatment was successful (as shown in Figure 2 ). The particle size of the product in water measured by a laser particle size analyzer was 161.0±0.5 nm, and the Zeta potential was 33.2 mV.

Experimental example

If the catalyst is used to treat water pollutants in an alkaline environment, it must have a good ability to agglomerate and settle pollutants in an alkaline environment. To this end, the particle size and Zeta potential were further measured in PBS balanced salt solution (pH=8.8), and the results are shown in Table 1. It can be seen that after the solid acid catalyst is added to the water system at this time, the average particle size is 1639±0.4nm, and the Zeta potential changes from positive to negative (-17.4mV). It shows that the agglomeration and settlement are obvious.

Table 1 The particle size and Zeta potential changes of ND solid acid in different media

medium Average particle size/nm Zeta potential/mV Deionized water (embodiment 1) 83.2±0.5 30.3 PBS balanced salt solution (embodiment 1) 1437±0.3 -18.2 Deionization (Example 2) 161.0±0.5 33.2 PBS balanced salt solution (embodiment 2) 1639±0.4 -17.4

Claims (6)

1. A nanometer diamond solid acid catalyst is characterized in that its structural formula is as follows: 2. prepare the method for nano diamond solid acid catalyst as claimed in claim 1, it is characterized in that, concrete steps are as follows: (1) carry out amino terminal modification to nano-diamond powder; (2) purifying and dispersing the nano-diamond powder modified by the amino terminal obtained in step (1); (3) performing sulfonation treatment on the product treated in step (2) to obtain a nano-diamond solid acid catalyst. 3. the method for preparing nano-diamond solid acid catalyst as claimed in claim 2, is characterized in that, described, in step (1), the specific steps that nano-diamond powder is carried out amino terminal modification are as follows: Single-crystal nano-diamonds with an average particle size of less than 100nm were ultrasonically cleaned with deionized water, ammonia water, and ethanol for 10 minutes, and then placed in the vacuum chamber of the low-pressure plasma processing equipment, and vacuumed to below 10Pa; then according to the flow ratio 2:1, hydrogen and nitrogen are introduced at the same time, and radio frequency electricity is applied to the gas in the vacuum chamber to obtain plasma. After 5-20 minutes of treatment, the sample is taken out to obtain nano-diamond powder modified with amino terminals on the surface. 4. the method for preparing nano-diamond solid acid catalyst as claimed in claim 2, is characterized in that, described, in described step (2), the specific step of purifying and dispersing the nano-diamond powder modified by amino terminal Proceed as follows: Weigh the zirconia powder according to 100-200 times the weight of the nano-diamond powder modified by the amino terminal, place ZrO2 at the bottom of the container, spread the nano _- diamond powder modified by the amino terminal evenly on it, and then add tetrahydrofuran or dimethylformamide, place the container in an ultrasonic processor for 2 hours, centrifuge to remove ZrO ₂ , and obtain a nano-diamond powder dispersion liquid modified by amino terminals. 5. the method for preparing nano-diamond solid acid catalyst as claimed in claim 4, is characterized in that, described tetrahydrofuran (THF) or dimethylformamide consumption are 5-10 times of all solid volumes. 6. the method for preparing nano-diamond solid acid catalyst as claimed in claim 2, is characterized in that, described sulfonation treatment, concrete steps are as follows: in the nano-diamond powder dispersion liquid that is modified by amino terminal, add The modified nano-diamond powder is 1,3-sultone twice the weight, ultrasonically treated at room temperature for 6-8 hours, centrifuged and washed with deionized water three times, and the precipitate is dried to obtain the final product.