Graphene quantum dot / TiO2 composite material and preparation method thereof

Abstract

The invention provides a graphene quantum dot / TiO2 composite material and a preparation method thereof, and belongs to the technical field of composite materials. Comprising the following steps: S1, dissolving citric acid, thiourea and boric acid in water, carrying out hydrothermal reaction, dialyzing, and freeze-drying non-permeated liquid to prepare S / B / N doped graphene quantum dots; s2, adding tetrabutyl titanate into water, adding L-carnitine, dropwise adding concentrated hydrochloric acid, heating and stirring for reaction, and calcining to obtain microporous titanium dioxide; s3, adding the microporous titanium dioxide into water, adding lanthanum salt and cerium salt, stirring and calcining to obtain doped microporous titanium dioxide; and S4, adding the S / B / N doped graphene quantum dots into water, carrying out uniform ultrasonic dispersion, adding the doped microporous titanium dioxide, and carrying out spray drying to prepare the graphene quantum dot / TiO2 composite material, which has good catalytic efficiency on visible light and even infrared light regions, increases catalytic active sites, improves the catalytic efficiency, and has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a graphene quantum dot / TiO 2 Composite material and method for preparing the same. Background Art

[0002] Nano-TiO 2 It is a new type of cheap N-type semiconductor material, also known as titanium dioxide. It has the characteristics of large specific surface area, strong magnetism, and ability to absorb ultraviolet rays. Under the action of light, its surface can release highly active photogenerated electron-hole pairs, and at the same time can generate highly oxidizing hydroxyl radicals (·OH) and superoxide radicals (·O 2- ), and it undergoes redox reaction with organic matter (formaldehyde, benzene, ammonia, etc.) and various bacteria in the air, degrading organic pollutants into CO 2 and H 2 O and other inorganic substances can effectively degrade toxic and harmful gases in the air and kill a variety of bacteria. It also has the functions of removing formaldehyde, deodorizing, anti-fouling, and purifying the air.

[0003] In nano-TiO 2 Among all the crystal forms, anatase has attracted extensive research in various industries due to its higher photocatalytic activity and controllable preparation. However, due to its large bandgap (about 3.2eV), it has a strong absorption capacity for ultraviolet light (≤380nm), but poor absorption for visible light. Ultraviolet light only accounts for 3%-5% of sunlight, so single TiO 2 The utilization rate of sunlight is extremely low. Secondly, the high recombination rate of photogenerated carriers also reduces its photocatalytic efficiency, which greatly limits its application.

[0004] Graphene has a two-dimensional honeycomb crystal structure formed by the close stacking of a single layer of carbon atoms. The unique and perfect structure of graphene gives it excellent electrical, mechanical, thermal and optical properties. Since there are many dangling bonds on the surface of graphene, it can be well bonded with the photocatalytic material. Secondly, graphene has a large specific surface area and high electron mobility, which increases the active points of the reaction, while reducing the recombination of electrons and holes, improving the photocatalytic efficiency. In addition, the presence of graphene narrows the band gap of the titanium dioxide photocatalytic material and increases the utilization rate of sunlight. Therefore, the photocatalytic efficiency can be improved by effectively compounding graphene and titanium dioxide photocatalytic materials. However, the specific surface area of ​​the graphene and titanium dioxide composite photocatalytic materials disclosed now is limited, and in the actual application of air purification, the composite photocatalytic material needs to be loaded on a substrate for use, the loading amount of the substrate is limited, and the contact area and contact time of the composite photocatalytic material on the substrate when the air passes through the purification device once are limited, and the composite photocatalytic material cannot completely and quickly degrade harmful substances such as bacteria and viruses in the air. Therefore, in order to broaden the practical application of composite photocatalytic materials, it is still necessary to develop a graphene and titanium dioxide composite photocatalytic material with a large specific surface area and higher photocatalytic efficiency.

[0005] Patent application No. 201010590547.3 discloses a graphene / nano-titanium dioxide composite and a preparation method thereof, wherein nano-titanium dioxide and graphene are dispersed in a water / ethanol solution of a certain proportion, and the nano-titanium dioxide and graphene in the dispersion are reacted by pressurizing and heating.

[0006] Patent application No. 201110225465.3 discloses a graphene / mesoporous titanium dioxide visible light catalyst and a preparation method thereof, wherein graphene oxide is added to glacial acetic acid and ultrasonically dispersed to obtain a dispersion of graphene oxide; a titanium source is added to the dispersion of graphene oxide and a graphene / mesoporous titanium dioxide nanocomposite visible light catalyst is prepared by a hydrothermal method.

[0007] Patent application No. 201210582986.9 discloses a method for preparing a graphene / titanium dioxide photocatalyst, wherein graphene oxide is added to a mixed solution of water and ethanol, the mixed solution is then added dropwise to chloroform containing tetrabutyl titanate, and the final mixed solution is reacted in a hydrothermal autoclave to prepare a graphene / titanium dioxide photocatalyst.

[0008] Patent application No. 201310287749.4 discloses a method for preparing a graphene and titanium dioxide composite material, wherein a precursor containing titanium ions is dissolved in anhydrous ethanol to prepare a solution, and then a graphene oxide solution is added, deposited, dried, and then the graphene and titanium dioxide composite material is obtained by a hydrothermal method.

[0009] However, although the composite material obtained by the above method can enable titanium dioxide to utilize the visible light region to a certain extent, the effect is not good. Summary of the invention

[0010] The purpose of the present invention is to provide a graphene quantum dot / TiO 2 The composite material and its preparation method have good catalytic efficiency in the visible light and even infrared light region, increase in catalytic active sites, improve catalytic efficiency, and have broad application prospects.

[0011] The technical solution of the present invention is achieved in this way: The present invention provides a graphene quantum dot / TiO 2 The method for preparing the composite material comprises the following steps: S1. Dissolving citric acid, thiourea and boric acid in water, performing a hydrothermal reaction, dialyzing and freeze-drying the non-permeated solution to obtain S / B / N-doped graphene quantum dots; S2. Tetrabutyl titanate was added to water, L-carnitine was added, and after stirring and mixing, concentrated hydrochloric acid was added dropwise, heated and stirred for reaction, centrifuged, washed, dried, and calcined to obtain microporous titanium dioxide; S3. adding microporous titanium dioxide to water, adding lanthanum salt and cerium salt, stirring and mixing, centrifuging, washing, drying, and calcining to obtain doped microporous titanium dioxide; S4. Add S / B / N doped graphene quantum dots into water, disperse them evenly with ultrasound, add doped microporous titanium dioxide, stir and mix evenly, spray dry to obtain graphene quantum dots / TiO 2 Composite materials.

[0012] As a further improvement of the present invention, the mass ratio of citric acid, thiourea and boric acid in step S1 is 10-15:2-4:1-2.

[0013] As a further improvement of the present invention, the temperature of the hydrothermal reaction in step S1 is 190-210° C., the time is 22-26 h, and the pore size of the dialysis bag used in the dialysis is 3000-4000 Da.

[0014] As a further improvement of the present invention, the mass ratio of tetrabutyl titanate, L-carnitine and concentrated hydrochloric acid in step S2 is 12-17:2-4:5-10.

[0015] As a further improvement of the present invention, the temperature of the heating and stirring reaction in step S2 is 60-80° C. and the time is 1-3 h.

[0016] As a further improvement of the present invention, the calcination temperature in step S2 is 450-550° C. and the calcination time is 3-5 hours.

[0017] As a further improvement of the present invention, in step S3, the lanthanum salt is lanthanum chloride or lanthanum nitrate, and the cerium salt is cerium chloride or cerium nitrate.

[0018] As a further improvement of the present invention, in step S3, the mass ratio of the microporous titanium dioxide, lanthanum salt and cerium salt is 15-20:1-2:2-3, the calcination temperature is 400-500° C., and the calcination time is 1-2 h.

[0019] As a further improvement of the present invention, the mass ratio of the S / B / N-doped graphene quantum dots to the doped microporous titanium dioxide in step S4 is 3-7:12-15.

[0020] The present invention further protects a graphene quantum dot / TiO prepared by the above preparation method 2 Composite materials.

[0021] The present invention has the following beneficial effects: In S / B / N doped graphene quantum dots, S, B, and N elements are doped on the graphene quantum dots to increase the number of holes in the graphene and the carrier concentration, thereby improving the electrical properties of the graphene quantum dots.

[0022] During the sol-gel reaction of microporous titanium dioxide, by adding a chiral porogen L-carnitine compound, the prepared titanium dioxide can form chiral micropores, which can induce light scattering and polarization effects, further expand the light absorption range of titanium dioxide to the visible light and even infrared bands, and enhance the photocatalytic activity.

[0023] Lanthanum salt and cerium salt are deposited on the surface of microporous titanium dioxide. Due to their unique 4f electron configuration, they improve the electronic and photoelectronic properties of graphene quantum dots and enhance the ability of titanium dioxide to utilize visible light, thereby improving the catalytic efficiency.

[0024] The composite system of S / B / N-doped graphene quantum dots and doped microporous titanium dioxide improves performance through the following synergistic effects: the high conductivity (conductivity > 100MS / m) and fast carrier migration ability of graphene quantum dots are combined to form an efficient electron transport network, which significantly reduces the TiO 2 The photogenerated electron-hole recombination rate is increased, thus improving the photocatalytic efficiency. The fluorescence characteristics of graphene quantum dots and the interface polarization effect of graphene work together to convert TiO 2 The light absorption range of graphene quantum dots is extended from ultraviolet light to visible light and even near-infrared regions, which greatly broadens the utilization efficiency. In addition, the surface functional groups of graphene quantum dots work together to enhance the absorption of pollutants (such as CO 2 , organic dyes), and achieve efficient degradation through interfacial reaction. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example 1

[0026] This embodiment provides a graphene quantum dot / TiO 2 The method for preparing the composite material comprises the following steps: S1. Dissolve 10g of citric acid, 2g of thiourea and 1g of boric acid in 500mL of water, perform hydrothermal reaction at 190℃ for 22h, dialyze for 72h in a dialysis bag with a pore size of 3000a, and freeze-dry the non-permeated liquid to obtain S / B / N-doped graphene quantum dots; S2. 12 g of tetrabutyl titanate was added to 500 mL of water, 2 g of L-carnitine was added, the mixture was stirred for 10 min, 5 g of concentrated hydrochloric acid was added dropwise, the mixture was heated to 60 ° C, stirred for 1 h, centrifuged, washed, dried, and calcined at 450 ° C for 3 h to obtain microporous titanium dioxide; S3. 15 g of microporous titanium dioxide was added to 200 mL of water, 1 g of lanthanum chloride and 2 g of cerium chloride were added, the mixture was stirred for 15 min, centrifuged, washed, dried, and calcined at 400 ° C for 1 h to obtain doped microporous titanium dioxide; S4. 3 g S / B / N doped graphene quantum dots were added to 200 mL water, ultrasonically dispersed at 2000 W for 15 min, 12 g doped microporous titanium dioxide was added, stirred and mixed for 15 min, and spray dried to obtain graphene quantum dots / TiO 2 Composite materials. Example 2

[0027] This embodiment provides a graphene quantum dot / TiO 2 The method for preparing the composite material comprises the following steps: S1. 15 g of citric acid, 4 g of thiourea and 2 g of boric acid were dissolved in 500 mL of water, and the reaction was carried out at 210 ° C for 26 h. The dialysis bag with a pore size of 4000 Da was dialyzed for 72 h, and the non-permeated liquid was freeze-dried to obtain S / B / N doped graphene quantum dots; S2. 17 g of tetrabutyl titanate was added to 500 mL of water, 4 g of L-carnitine was added, the mixture was stirred for 10 min, 10 g of concentrated hydrochloric acid was added dropwise, the mixture was heated to 80 ° C, stirred for 3 h, centrifuged, washed, dried, and calcined at 550 ° C for 5 h to obtain microporous titanium dioxide; S3. 20 g of microporous titanium dioxide was added to 200 mL of water, 2 g of lanthanum nitrate and 3 g of cerium nitrate were added, the mixture was stirred for 15 min, centrifuged, washed, dried, and calcined at 500 ° C for 2 h to obtain doped microporous titanium dioxide; S4. 7 g S / B / N doped graphene quantum dots were added to 200 mL water, ultrasonically dispersed at 2000 W for 15 min, 15 g doped microporous titanium dioxide was added, stirred and mixed for 15 min, and spray dried to obtain graphene quantum dots / TiO 2 Composite materials. Example 3

[0028] This embodiment provides a graphene quantum dot / TiO 2 The method for preparing the composite material comprises the following steps: S1. 12 g of citric acid, 3 g of thiourea and 1.5 g of boric acid were dissolved in 500 mL of water, and the mixture was hydrothermally reacted at 100 °C for 24 h. The mixture was dialyzed in a dialysis bag with a pore size of 3500 Da for 72 h. The non-permeated liquid was freeze-dried to obtain S / B / N-doped graphene quantum dots. S2. 15 g of tetrabutyl titanate was added to 500 mL of water, 3 g of L-carnitine was added, the mixture was stirred for 10 min, 7 g of concentrated hydrochloric acid was added dropwise, the mixture was heated to 70 ° C, stirred for 2 h, centrifuged, washed, dried, and calcined at 500 ° C for 4 h to obtain microporous titanium dioxide; S3. 17 g of microporous titanium dioxide was added to 200 mL of water, 1.5 g of lanthanum chloride and 2.5 g of cerium chloride were added, stirred and mixed for 15 min, centrifuged, washed, dried, and calcined at 450 ° C for 1.5 h to obtain doped microporous titanium dioxide; S4. 5 g S / B / N doped graphene quantum dots were added to 200 mL water, ultrasonically dispersed at 2000 W for 15 min, 13 g doped microporous titanium dioxide was added, stirred and mixed for 15 min, and spray dried to obtain graphene quantum dots / TiO 2 Composite materials.

[0029] Comparative Example 1 Compared with Example 3, the difference is that thiourea is not added in step S1.

[0030] The details are as follows: S1. 12 g of citric acid and 4.5 g of boric acid were dissolved in 500 mL of water, and the mixture was hydrothermally reacted at 100 °C for 24 h. The mixture was dialyzed in a dialysis bag with a pore size of 3500 Da for 72 h. The non-permeated liquid was freeze-dried to obtain B-doped graphene quantum dots. S2. 15 g of tetrabutyl titanate was added to 500 mL of water, 3 g of L-carnitine was added, the mixture was stirred for 10 min, 7 g of concentrated hydrochloric acid was added dropwise, the mixture was heated to 70 ° C, stirred for 2 h, centrifuged, washed, dried, and calcined at 500 ° C for 4 h to obtain microporous titanium dioxide; S3. 17 g of microporous titanium dioxide was added to 200 mL of water, 1.5 g of lanthanum chloride and 2.5 g of cerium chloride were added, stirred and mixed for 15 min, centrifuged, washed, dried, and calcined at 450 ° C for 1.5 h to obtain doped microporous titanium dioxide; S4. 5 g B-doped graphene quantum dots were added to 200 mL of water, ultrasonically dispersed at 2000 W for 15 min, 13 g doped microporous titanium dioxide was added, stirred and mixed for 15 min, and spray dried to obtain graphene quantum dots / TiO 2 Composite materials.

[0031] Comparative Example 2 Compared with Example 3, the difference is that no boric acid is added in step S1.

[0032] The details are as follows: S1. 12 g of citric acid and 4.5 g of thiourea were dissolved in 500 mL of water, and the mixture was hydrothermally reacted at 100 °C for 24 h. The mixture was dialyzed in a dialysis bag with a pore size of 3500 Da for 72 h. The non-permeated liquid was freeze-dried to obtain S / N-doped graphene quantum dots. S2. 15 g of tetrabutyl titanate was added to 500 mL of water, 3 g of L-carnitine was added, the mixture was stirred for 10 min, 7 g of concentrated hydrochloric acid was added dropwise, the mixture was heated to 70 ° C, stirred for 2 h, centrifuged, washed, dried, and calcined at 500 ° C for 4 h to obtain microporous titanium dioxide; S3. 17 g of microporous titanium dioxide was added to 200 mL of water, 1.5 g of lanthanum chloride and 2.5 g of cerium chloride were added, stirred and mixed for 15 min, centrifuged, washed, dried, and calcined at 450 ° C for 1.5 h to obtain doped microporous titanium dioxide; S4. 5 g S / N doped graphene quantum dots were added to 200 mL water, ultrasonically dispersed at 2000 W for 15 min, 13 g doped microporous titanium dioxide was added, stirred and mixed for 15 min, and spray dried to obtain graphene quantum dots / TiO 2 Composite materials.

[0033] Comparative Example 3 Compared with Example 3, the difference is that L-carnitine is not added in step S2.

[0034] The details are as follows: S1. 12 g of citric acid, 3 g of thiourea and 1.5 g of boric acid were dissolved in 500 mL of water, and the mixture was hydrothermally reacted at 100 °C for 24 h. The mixture was dialyzed in a dialysis bag with a pore size of 3500 Da for 72 h. The non-permeated liquid was freeze-dried to obtain S / B / N-doped graphene quantum dots. S2. 15 g of tetrabutyl titanate was added to 500 mL of water, stirred and mixed for 10 min, 7 g of concentrated hydrochloric acid was added dropwise, heated to 70 ° C, stirred and reacted for 2 h, centrifuged, washed, dried, and calcined at 500 ° C for 4 h to obtain titanium dioxide; S3. 17 g of titanium dioxide was added to 200 mL of water, 1.5 g of lanthanum chloride and 2.5 g of cerium chloride were added, stirred and mixed for 15 min, centrifuged, washed, dried, and calcined at 450 ° C for 1.5 h to obtain doped titanium dioxide; S4. 5 g S / B / N doped graphene quantum dots were added to 200 mL water, ultrasonically dispersed at 2000 W for 15 min, 13 g doped titanium dioxide was added, stirred and mixed for 15 min, and spray dried to obtain graphene quantum dots / TiO 2 Composite materials.

[0035] Comparative Example 4 Compared with Example 3, the difference is that step S3 is not performed.

[0036] The details are as follows: S1. 12 g of citric acid, 3 g of thiourea and 1.5 g of boric acid were dissolved in 500 mL of water, and the mixture was hydrothermally reacted at 100 °C for 24 h. The mixture was dialyzed in a dialysis bag with a pore size of 3500 Da for 72 h. The non-permeated liquid was freeze-dried to obtain S / B / N-doped graphene quantum dots. S2. 15 g of tetrabutyl titanate was added to 500 mL of water, 3 g of L-carnitine was added, the mixture was stirred for 10 min, 7 g of concentrated hydrochloric acid was added dropwise, the mixture was heated to 70 ° C, stirred for 2 h, centrifuged, washed, dried, and calcined at 500 ° C for 4 h to obtain microporous titanium dioxide; S3. 5 g S / B / N doped graphene quantum dots were added to 200 mL water, ultrasonically dispersed at 2000 W for 15 min, 13 g microporous titanium dioxide was added, stirred and mixed for 15 min, and spray dried to obtain graphene quantum dots / TiO 2 Composite materials.

[0037] Comparative Example 5 Compared with embodiment 3, the difference is that only step S2 is included.

[0038] The details are as follows: 15 g of tetrabutyl titanate was added to 500 mL of water, 3 g of L-carnitine was added, the mixture was stirred for 10 min, 7 g of concentrated hydrochloric acid was added dropwise, the mixture was heated to 70° C., the mixture was stirred for 2 h, the mixture was centrifuged, washed, dried, and calcined at 500° C. for 4 h to obtain microporous titanium dioxide.

[0039] Test Example 1 100 mL of 40 mg / L methyl blue solution was placed in a beaker, and then 0.2 g of graphene quantum dots / TiO prepared in Examples 1-3 or Comparative Examples 1-4 was added to the system. 2 The composite material and the microporous titanium dioxide prepared in Comparative Example 5 were immersed for 24 hours and then moved to a dark box. After irradiating the suspension with a xenon lamp (300W) for 1 hour, 5 mL of the solution was taken out and the absorbance at a wavelength of 620 nm was measured with a spectrophotometer. The apparent degradation rate was calculated according to formula (1): (1) In the formula, is the initial absorbance of methylene blue, is the absorbance of methyl blue after catalytic degradation The results are shown in Table 1.

[0040] Table 1

[0041] As can be seen from the above table, the graphene quantum dots / TiO 2 The composite material has a good effect of utilizing the light zone for photocatalytic degradation.

[0042] Test Example 2 The graphene quantum dots / TiO prepared in Examples 1-3 or Comparative Examples 1-4 were measured using a 3-FLEX 3500 multi-station high-throughput gas adsorption instrument. 2 The specific surface areas of the composite material and the microporous titanium dioxide prepared in Comparative Example 5 are shown in Table 2.

[0043] Table 2

[0044] As can be seen from the above table, the graphene quantum dots / TiO 2 The composite material has a larger specific surface area.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a graphene quantum dot / TiO2 composite material, characterized in that: The following steps are involved: S1. Dissolving citric acid, thiourea and boric acid in water, performing a hydrothermal reaction, dialyzing and freeze-drying the non-permeated solution to obtain S / B / N-doped graphene quantum dots; S2. Tetrabutyl titanate was added to water, L-carnitine was added, and after stirring and mixing, concentrated hydrochloric acid was added dropwise, heated and stirred for reaction, centrifuged, washed, dried, and calcined to obtain microporous titanium dioxide; S3. adding microporous titanium dioxide to water, adding lanthanum salt and cerium salt, stirring and mixing, centrifuging, washing, drying, and calcining to obtain doped microporous titanium dioxide; S4. Add S / B / N doped graphene quantum dots into water, disperse them evenly by ultrasonication, add doped microporous titanium dioxide, stir and mix evenly, spray dry, and obtain a graphene quantum dot / TiO2 composite material.

2. The preparation method according to claim 1, characterized in that: The mass ratio of citric acid, thiourea and boric acid in step S1 is 10-15:2-4:1-2.

3. The preparation method according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step S1 is 190-210° C., the time is 22-26 hours, and the pore size of the dialysis bag used in the dialysis is 3000-4000 Da.

4. The preparation method according to claim 1, characterized in that: The mass ratio of tetrabutyl titanate, L-carnitine and concentrated hydrochloric acid in step S2 is 12-17:2-4:5-10.

5. The preparation method according to claim 1, characterized in that: The temperature of the heating and stirring reaction in step S2 is 60-80° C. and the time is 1-3 h.

6. The preparation method according to claim 1, characterized in that: The calcination temperature in step S2 is 450-550° C. and the calcination time is 3-5 hours.

7. The preparation method according to claim 1, characterized in that: In step S3, the lanthanum salt is lanthanum chloride or lanthanum nitrate, and the cerium salt is cerium chloride or cerium nitrate.

8. The preparation method according to claim 1, characterized in that: In step S3, the mass ratio of microporous titanium dioxide, lanthanum salt and cerium salt is 15-20:1-2:2-3, the calcination temperature is 400-500° C., and the calcination time is 1-2 hours.

9. The preparation method according to claim 1, characterized in that: The mass ratio of the S / B / N-doped graphene quantum dots to the doped microporous titanium dioxide in step S4 is 3-7:12-15.

10. A graphene quantum dot / TiO2 composite material prepared by the preparation method according to any one of claims 1 to 9.

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