CN109319770B

CN109319770B - Method for adjusting pH value of solution based on graphene quantum dots

Info

Publication number: CN109319770B
Application number: CN201811059194.7A
Authority: CN
Inventors: 孙成华; 徐勇军
Original assignee: Dongguan University of Technology
Current assignee: Dongguan University of Technology
Priority date: 2018-09-12
Filing date: 2018-09-12
Publication date: 2020-04-10
Anticipated expiration: 2038-09-12
Also published as: CN109319770A

Abstract

The invention relates to the field of graphene quantum dots, in particular to a method for adjusting the pH value of a solution based on graphene quantum dots, which comprises the following steps of a preparing graphene quantum dots, b taking the graphene quantum dots prepared in the step a to adjust the pH value of the solution under illumination, wherein the step of preparing the graphene quantum dots comprises ① taking a graphite powder block to be mechanically mixed with a molten salt catalyst, ② taking a mixed material in the step ① to be subjected to preheating treatment and heat preservation, ③ taking the mixed material subjected to heat preservation in the step ② to be directly heated and subjected to heat preservation, ④ cooling the mixed material in the step ③ to room temperature and then carrying out water soaking treatment to obtain a suspension, and ⑤ taking the suspension in the step ④ to obtain a graphene quantum dot product through centrifugal filtration.

Description

Method for adjusting pH value of solution based on graphene quantum dots

Technical Field

The invention relates to the field of graphene quantum dots, in particular to a method for adjusting the pH value of a solution based on graphene quantum dots.

Background

The pH value of the solution is adjusted by adding a substance containing H + or OH-ions to perform a neutralization reaction with OH-ions or H + in the solution. This regulation is irreversible. The innovation of the invention is that a large amount of hydrogen sulfate is introduced through the edge of the quantum dot, and because the nano size of the quantum dot is high in the content of edge atoms, the content of the hydrogen sulfate introduced through the quantum dot is extremely high. Meanwhile, the size effect of the quantum dots causes the forbidden band of the graphene to be opened, so that the graphene has semiconductor characteristics and light absorption performance. Under illumination, the photo-generated electrons induce further ionization of hydrogen sulfate to release hydrogen ions (H +), and the pH of the solution is adjusted. A large number of bacteria exist and propagate only in a characteristic acid-base environment, and once the acidity of the solution is effectively enhanced, the bacteria are difficult to kill. Different from the common acid-base regulation, the method is induced by light, once the light source is closed, photo-generated thermoelectrons are not provided any more, the bisulfate ionization reverse reaction is generated, and the solution and the quantum dots return to the initial state again. Therefore, the light-operated acid-base regulation and control sterilization is suitable for drinking water sterilization, sewage treatment and public sterilization.

Graphene quantum dots (Graphene quantum dots) are quasi-zero-dimensional nano materials, and the movement of electrons in the Graphene quantum dots in all directions is limited, so that the quantum confinement effect is particularly remarkable and the Graphene quantum dots have many unique properties. This will bring revolutionary changes to the fields of electronics, optoelectronics, and electromagnetism. The method is applied to the aspects of solar cells, electronic equipment, optical dyes, biomarkers, composite particle systems and the like. Such as to adjust the acidity or basicity of the solution.

For the preparation of graphene quantum dots, two strategies of 'bottom-up' or 'top-down' are generally adopted at present, wherein the former takes organic matters as raw materials and obtains large-size aromatic hydrocarbons and even graphene quantum dots through synthesis, and then takes graphite or graphene as raw materials and obtains the graphene quantum dots through cutting, oxidation and strong acid treatment.

In the synthesis from bottom to top, the product often has the problems of low graphitization degree, more impurities and difficult separation, and the like, most of the upper and lower methods need to adopt graphene as a material and carry out various cutting treatments, so the cost is high, the product often contains a large amount of oxygen-containing optical energy groups and defects, and when the product is used for adjusting the pH value of a solution, the detection precision is low, and the method is not suitable for large-scale production.

Disclosure of Invention

In order to solve the problems, the invention provides a method for adjusting the pH value of a solution based on graphene quantum dots, which has high detection precision and is suitable for large-scale production.

The technical scheme adopted by the invention is as follows: the method for adjusting the pH value of the solution based on the graphene quantum dots is characterized by comprising the following steps: the method comprises the following steps of a, preparing graphene quantum dots; b. b, taking the graphene quantum dots prepared in the step a, and adjusting the pH value of the solution under illumination

The technical scheme is further improved in that in the step a, the preparation method of the graphene quantum dot comprises the following steps of ① taking a graphite powder block and mechanically mixing the graphite powder block with a molten salt catalyst, ② taking the mixed material in the step ①, carrying out preheating treatment and heat preservation, ③ taking the mixed material after the heat preservation in the step ②, directly heating and preserving the heat, ④ cooling the mixed material in the step ③ to room temperature, carrying out water soaking treatment to obtain a suspension, and ⑤ taking the suspension in the step ④, and carrying out centrifugal filtration to obtain a graphene quantum dot product.

The technical scheme is further improved in that in step ①, the mass ratio of the graphite powder block to the molten salt catalyst is 1: 2-1: 8.

The further improvement of the technical scheme is that in step ①, the graphite powder block is industrial grade graphite powder, the ash content is not more than 0.05, the moisture content is not more than 0.02, the carbon content is more than 99%, and the grain size is 500-15000 meshes.

In a further improvement of the above technical solution, in step ①, the molten salt catalyst is cesium carbonate molten salt.

The further improvement of the technical proposal is that in the step ②, the temperature of the pretreatment and the heat preservation is 300-450 ℃, and the heat preservation time is 0.5-1.5 h.

The further improvement of the technical proposal is that in the step ③, the temperature for heat preservation is 550-650 ℃, and the time for heat preservation is 1-2 h.

In step ④, deionized water is used for soaking treatment, and suspension is obtained by ultrasonic separation.

The technical proposal is further improved in that in step ⑤, the raw materials are firstly centrifuged for 20-40min to remove the residual starting materials, and then dialyzed for 1-3 d.

The invention has the beneficial effects that:

1. the pesticide detection mode is realized based on the graphene quantum dots, has high detection precision and low manufacturing cost, and is suitable for large-scale production.

2. For the preparation method of the graphene quantum dot, on one hand, the preparation method provided by the invention takes the graphite powder block as a raw material, realizes efficient cutting of a carbon structure in the graphite powder block in a molten state by directly carrying out molten salt catalysis, does not introduce strong acid or oxygen in the whole process, can be adjusted by controlling the temperature and time of the molten salt, and the obtained graphene quantum dot has the advantages of high graphitization degree, clean edge, no impurity functional group, high purity and good quality of a finished product, low manufacturing cost and suitability for large-scale production. In the second aspect, the preparation method of the invention has simple process and easy realization of production conditions, and is suitable for large-scale production. The existence of a large amount of basic ions (Cs) in the molten salt⁺) CsO can efficiently etch the C-C bonding structure, and CO can be generated in the molten salt state₃ ^2-The root ions can stabilize the highly activated carbon, contributing to the retention and formation of graphene sheets.

3. In the step ①, the mass ratio of the graphite powder block to the molten salt catalyst is 1: 2-1: 8, preferably 1: 5, if the content of the molten salt catalyst is too low, the graphite powder block cannot be sufficiently catalyzed, and if the content of the molten salt catalyst is too high, excessive molten salt catalyst interferes with cutting of the graphite powder block, and experiments prove that when the mass ratio of the graphite powder block to the molten salt catalyst is 1: 5, the carbon structure in the graphite powder block can be sufficiently and efficiently cut, and the finished product has high purity and good quality.

4. In step ①, the graphite powder block is industrial grade graphite powder, the ash content is not more than 0.05, the water content is not more than 0.02, the carbon content is more than 99%, and 500-15000 meshes, and the graphite powder is conventionally available and low in cost.

5. In step ①, the molten salt catalyst is cesium carbonate molten salt, the melting point of cesium carbonate is 580-600 ℃, and graphite sheet glass and cutting can be realized at 600 ℃ by selecting the molten salt.

6. In step ②, the temperature for pretreatment is 300-450 deg.C, and the time for heat preservation is 0.5-1.5 h.

7. In step ③, the temperature is 550-650 ℃, the time is 1-2h, at this temperature, the cesium carbonate catalyst is in a molten state, a large amount of basic radical ions (Cs +) are released and exist in active structures such as CsO, which is helpful for cutting C-C bonds, the time is 1-2h, too long treatment can cause excessive cutting of C-C bonds, carbon atoms tend to form amorphous structures, and too short time can cause insufficient cutting, which is difficult to form quantum dots.

8. In step ④, deionized water is used for soaking, and suspension is obtained by ultrasonic separation, preferably ultrasonic (100W, 40kHz) for 1 hour, to improve the purity of the finished graphene quantum dots.

9. In step ⑤, centrifuging for 20-40min to remove residual starting material, dialyzing for 1-3d, preferably centrifuging the suspension at 10000 rpm for 30min to remove residual starting material, and dialyzing for 2 days by a dialysis bag (with a retention molecular weight of 500-1000 Da) to improve the purity of the finished graphene quantum dot.

10. The graphene quantum dot prepared by the method has the advantages of high graphitization degree, clean edge, no impurity functional group and high finished product purity and quality, and has wide application in the field of biological and chemical sensors due to the size effect and the edge effect.

Drawings

FIG. 1 is an electron micrograph, a product solution macroscopic view and a reaction schematic view of a raw material graphite powder block and boron nitride;

FIG. 2 is a high-resolution electron microscope image of a finished graphene quantum dot;

FIG. 3 is a diagram of XRD, Raman and XPS analysis results of the finished graphene quantum dots;

FIG. 4 is a high-resolution electron microscope image of the finished boron nitride quantum dot;

FIG. 5 is a diagram of the results of XRD, Raman and XPS analysis of the boron nitride quantum dots.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1: preparation of graphene quantum dots

The preparation method of the graphene quantum dot comprises the following steps of ① taking graphite powder blocks and mechanically mixing with a molten salt catalyst, ② taking the mixed material obtained in the step ①, carrying out preheating treatment and heat preservation, ③ taking the mixed material obtained after the heat preservation in the step ②, directly heating and preserving the heat, ④ cooling the mixed material obtained in the step ③ to room temperature, carrying out water soaking treatment to obtain a suspension, and ⑤ taking the suspension obtained in the step ④, and carrying out centrifugal filtration to obtain a graphene quantum dot product.

In step ①, the mass ratio of the graphite powder lumps to the molten salt catalyst is 1: 2 to 1: 8, preferably 1: 5 in this embodiment.

In step ①, the graphite powder block is industrial grade graphite powder, the ash content of the graphite powder block of the embodiment is not more than 0.05, the moisture content is not more than 0.02, the carbon content is more than 99%, and the particle size is 500-15000 mesh.

In step ①, the molten salt catalyst of the present embodiment is cesium carbonate molten salt.

In step ②, the temperature of the pretreatment is 300-.

In step ③, the temperature is kept at 620 ℃ for 1.5 h.

In step ④, deionized water is used for soaking treatment, and suspension is obtained by ultrasonic separation, preferably ultrasonic (100W, 40kHz) for 1 hour, so as to improve the purity of the finished graphene quantum dots.

In step ⑤, centrifuging for 20-40min to remove residual starting material, dialyzing for 1-3d, preferably centrifuging the suspension at 10000 rpm for 30min to remove residual starting material, and dialyzing for 2 days by a dialysis bag (with a retention molecular weight of 500-1000 Da) to improve the purity of the finished graphene quantum dot.

Example 2: preparation of boron nitride quantum dots

The preparation method of the boron nitride quantum dot is the same as the example 1 except that the raw material is hexagonal boron nitride.

And (4) analyzing results:

FIG. 1 is the electron microscope photograph, the macroscopic view of the product solution and the reaction schematic diagram of the raw material graphite powder block and boron nitride.

As can be seen from fig. 1, a schematic preparation process of the graphene quantum dot and the boron nitride quantum dot. Diluted GQDS (5mg/ml) was clear, with black particles suspended. The low water solubility and metallic luster means that it has less hydrophilic functional groups, which is completely different from the Carbon Quantum Dots (CQDS) reported previously. BNQDs (5mg/ml) showed milky white color. Both GQDs and BNQDs are prone to precipitation and aggregation. This is a result of the small number of hydrophilic functional groups on the surface of GQDs and BNQDS, and is confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS).

Fig. 2 is a high-resolution electron microscope image of the finished graphene quantum dots.

As can be seen from fig. 2, Transmission Electron Microscopy (TEM) showed that the GQDS obtained by the present preparation method was uniform in diameter, and from the overall size distribution diagram 2a, it can be seen that the size range of GQDS was 2 to 4nm, and most (58%) was 3 nm. Fig. 2b is a High Resolution Transmission Electron Microscope (HRTEM) image of a single GQD with high crystallinity, jagged edges, and a lattice spacing of 0.199 nm, which is well matched to the (012) spacing of graphene. As shown in fig. 2c, the bright spots from the corresponding Fast Fourier Transform (FFT) pattern of a single GQDS demonstrate excellent crystallinity.

As shown in fig. 3, fig. 3a to fig. 3d are XRD, raman and XPS analysis results of the finished graphene quantum dots.

The XRD patterns of graphite and prepared GQDS are shown in fig. 3 a. The most intense diffraction peak at 26.6 ° corresponds to the representative (002) peak of graphite. This peak is significantly reduced, but still sharp, rather than the broad peak of GQDS, indicating that the GQDS obtained is not single-layer graphene, but a nanocluster of several layers of graphite. The 2 sitar-41-48 ° range was chosen to determine stack modification. The characteristic (100) -2H and (101) -2H peaks indicate the 2H phase of the graphite. However, after breaking into nanoparticles, the (101) -3R and (012) -3R peaks indicate stacking of 2H and 3R in GQDs, which may be the result of sliding and twisting of the layers during dicing. Raman spectroscopy (fig. 3b) was also used to study the structure of graphite and GQDS. Reduced Graphene Oxide (RGO) is shown for comparison. The relative intensity of the D band and G band (ID/Ig) of RGO is 0.91, which is well consistent with the literature. Graphite has no distinct "disordered" D band, but for a GQDS with an Id/Ig ratio of 0.13, a small D band appears. The G peak is red-shifted compared to graphite, while RGO is blue-shifted. Raman spectroscopy results show that GQDS produces few defects, mainly from edge trim.

XPS was also used to probe the chemical composition of GQDS. From the XPS measurement spectrum (FIG. 3C), a predominant C1S peak at ca.284.8 eV and an O1S peak at 532.8eV were detected at an atomic ratio of 1: 0.07. By fitting the area of the curve of the high resolution C1S spectrum, the relative contents of C C, C-C, C-O and COOH were calculated to be 36%, 18%, 37.9% and 8.2%, respectively. This confirms the advantage of SP2 hybrid carbon, and the SP3 carbon and oxygen-containing functional groups should come from the cut edge and adventitious carbon of CS2CO 3.

FIG. 4 is a high-resolution electron microscope image of the finished boron nitride quantum dots.

TEM images of BNQDS (FIG. 4a) show uniform size from 2nm to 4 nm. HRTEM images of a single BNQDS (fig. 4b) show high crystallinity and 0.214nm of lattice fringes, which correspond to the (100) spacing of H-BN. Good crystallinity was confirmed from the bright spots of single BNQDS (fig. 4c) of the corresponding Fast Fourier Transform (FFT) pattern.

As shown in fig. 5, fig. 5 a-5 f are XRD, raman and XPS analysis results of the finished boron nitride quantum dots.

FIG. 5(a) shows XRD spectra of a number of H-BN and the BNQDs prepared. All characteristic peaks of BNQDS are weaker compared to bulk H-BN, and the intensity of the (002) peak is weaker than that of H-BN by more than 5 times, indicating that the number of layers is significantly reduced, but the multi-layer characteristic still exists.

Raman spectroscopy of BNQDS shows that the E2G phonon peak at about 1367cm-1 is much smaller than the bulk H-BN, and its half-width is slightly larger in the half-maximum value (HWHM) of 11.2cm-1 compared to the bulk H-BN of 10 cm-1.

The HWHM of the obtained BNQDs is smaller than that of the BNQDs prepared by the previously reported solvothermal method (12.3cm-1) [6C ] and the potassium intercalation method (11-12cm-1) [6A ], which indicates that the molten salt flux method is less destructive to the lamellar structure. According to XPS measurement spectra (fig. 5a), the prepared BNQDS contains boron, nitrogen and carbon and oxygen. High resolution XPS C1S spectra can be modeled as four peaks, C-B (at 283.3eV), adventitious C-C/C/C (at 284.6eV), C-N (at 285.6eV) and C-N/C-O-B (at 291.3eV). The C1S spectrum indicates that the carbon peak is mainly contributed by adventitious carbon. High resolution B1S and N1S spectra were fitted using a multimodal gaussian method. The relative strengths indicate the predominance of B-N bonds and a small number of oxygen-containing bonds.

And (4) conclusion: as can be seen from the figures, the graphene quantum dot or boron nitride quantum dot product is proved to contain a good graphite flake structure through X-ray detection; the transmission electron microscope analysis shows that most of the graphene quantum dots are between 2 and 5 nanometers and belong to a multi-layer structure; raman detection shows that the D mode of the quantum dot is very low, the D/G mode ratio is far lower than that of graphene oxide, and the product is proved to have high graphitization degree and few defects; x-ray photoelectron spectrum and infrared spectrum detection prove that the oxygen-containing functional groups in the product are very low and can not be detected almost, which indicates that the finished product has high purity and good quality.

The graphene quantum dots or boron nitride quantum dots prepared in the embodiment 1 or the embodiment 2 are adopted to adjust the pH value of the solution, and specifically the method comprises the following steps: taking the graphene/boron nitride quantum dots, functionalizing edge functional groups of the graphene/boron nitride quantum dots, and then adjusting the pH value of the solution. By adopting the method, the prepared graphene/boron nitride quantum dots have better purity, higher graphitization degree, less defects and good quality, so that the pH value of the solution can be flexibly adjusted, particularly the concentration under a specific illumination condition.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The method for adjusting the pH value of the solution based on the graphene quantum dots is characterized by comprising the following steps: the method comprises the following steps of a, preparing graphene quantum dots; b. and (b) taking the graphene quantum dots prepared in the step (a) and adjusting the pH value of the solution under illumination.

2. The method for adjusting the pH value of the solution based on the graphene quantum dots according to claim 1, wherein in the step a, the preparation of the graphene quantum dots comprises the steps of ① taking a graphite powder block to be mechanically mixed with a molten salt catalyst, ② taking the mixed material in the step ① to be subjected to preheating treatment and heat preservation, ③ taking the mixed material after the heat preservation in the step ② to be directly heated and heat preserved, ④ cooling the mixed material in the step ③ to room temperature, performing water soaking treatment to obtain a suspension, and ⑤ taking the suspension in the step ④ to be subjected to centrifugal filtration to obtain a graphene quantum dot product.

3. The method for adjusting the pH value of the solution based on the graphene quantum dots according to claim 2, wherein in the step ①, the mass ratio of the graphite powder block to the molten salt catalyst is 1: 2-1: 8.

4. The method for adjusting the pH value of a solution based on graphene quantum dots as claimed in claim 3, wherein in step ①, the graphite powder block is industrial-grade graphite powder, the ash content is not more than 0.05, the water content is not more than 0.02, the carbon content is more than 99%, and the particle size is 500-15000 meshes.

5. The method for adjusting the pH value of the solution based on the graphene quantum dots according to claim 4, wherein in the step ①, the molten salt catalyst is cesium carbonate molten salt.

6. The method for adjusting the pH value of a solution based on graphene quantum dots according to claim 5, wherein in the step ②, the temperature for the pretreatment and the heat preservation is 300-450 ℃, and the heat preservation time is 0.5-1.5 h.

7. The method for adjusting the pH value of a solution based on graphene quantum dots according to claim 6, wherein in the step ③, the temperature is 550-650 ℃ and the holding time is 1-2 h.

8. The method for adjusting the pH value of a solution based on graphene quantum dots according to claim 7, wherein in the step ④, deionized water is adopted for treatment during soaking treatment, and a suspension is obtained through ultrasonic separation.

9. The method for adjusting the pH value of a solution based on graphene quantum dots according to claim 8, wherein in step ⑤, the solution is centrifuged for 20-40min to remove residual starting materials, and then dialyzed for 1-3 d.