CN106861744A - A kind of nitrogen sulphur is co-doped with the one-step method for synthesizing of titanium dioxide/graphene quantum dot heterostructures - Google Patents

Abstract

The invention discloses a one-step synthesis method of nitrogen and sulfur co-doped titanium dioxide/graphene quantum dot heterojunction. The preparation method adopted in the present invention can not only synthesize the co-doped modified binary system in one step, but also can co-dope titanium dioxide and nitrogen with nitrogen and sulfur, and the sulfur co-doped graphene quantum dots can be made through strong chemical bonds. It is tightly compounded together. The invention is mainly applied in the field of photocatalytic degradation, adopts visible light to degrade methylene blue, and detects the photocatalytic performance of the composite material through a degradation curve. Due to the excellent visible light catalytic activity of the composite material, the photocatalytic efficiency is greatly improved compared with single titanium dioxide, and it is environmentally friendly, does not introduce heavy metal ions, does not cause secondary pollution to treated water resources, and has excellent circulation stability.

Description

One-step synthesis of a nitrogen-sulfur co-doped titania/graphene quantum dot heterojunction method

technical field

The invention belongs to the technical field of nanomaterial preparation, and in particular relates to a preparation method for one-step synthesis of nitrogen-sulfur co-doped titanium dioxide/nitrogen-sulfur co-doped graphene quantum dot composite material and its photocatalytic degradation application.

technical background

With the development of industrialization, environmental problems have become an important factor restricting economic development. Especially for water pollution, it affects people's lives. Due to the massive discharge of organic dyes in industry, serious water pollution problems are caused. Moreover, there are many kinds of dyes, which are highly polluting and difficult to completely degrade. Therefore, there is an urgent need for a catalyst with wide application range, low raw material cost, wide sources and no secondary pollution. Titanium dioxide is the most widely used catalyst in industry due to its strong oxidizing properties, low cost and non-toxicity. However, titanium dioxide has a wide band gap (3.2eV), so it can only absorb ultraviolet light, and has a high recombination efficiency of electrons and holes, which restricts its further development and practical application.

Graphene quantum dots are an emerging material that has both the excellent electron transport properties of graphene and the performance of semiconductors. Combining with titanium dioxide can broaden its light absorption range to a certain extent. However, the tedious preparation and compounding process requires more energy. How to achieve one-step modification and successfully prepare composite materials has become the key to the problem.

The purpose of the present invention is to address the deficiencies in the prior art, to provide a one-step synthesis of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material preparation method. And it is applied in the field of photocatalytic degradation of dyes. The composite material has the characteristics of short synthesis period, co-doping modification, high catalytic activity and good stability.

Contents of the invention

The technical problem to be solved in the present invention is to overcome the deficiencies of the prior art and provide a one-step synthesis method of nitrogen-sulfur co-doped titanium dioxide/graphene quantum dot heterojunction, which can degrade the dye under visible light without It will cause secondary pollution.

The purpose of the present invention is achieved through the following technical solutions:

A one-step synthesis method of nitrogen-sulfur co-doped titanium dioxide/graphene quantum dot heterojunction, the steps of which include:

(1) Dissolve citric acid and thiourea in dimethylformamide at a molar ratio of 2:1 to 1:3, and the concentration of citric acid is 12.5mol/L.

(2) Titanium dioxide (P25) was added to the solution obtained in step 1, and stirred to obtain a suspension, the concentration of titanium dioxide was 15.6 mol/L.

(3) Move the suspension obtained in step 2 to a reaction kettle, react at 180°C for 6 hours, and centrifuge to obtain a gray product.

(4) Wash the gray products obtained from the reaction in step 3 respectively, and then dry them in vacuum to finally obtain a nitrogen-sulfur co-doped titanium dioxide/nitrogen-sulfur co-doped graphene quantum dot composite material.

Further, the optimal molar ratio of citric acid and thiourea in step 1 is 1:1.

Further, in step 3, centrifugal separation is carried out at 8000-9000 rpm for 20-30 minutes.

Further, in step 4, wash with ethanol and ultrapure water respectively twice, and centrifuge at 8000-9000 rpm for 10-20 minutes.

The beneficial effects of the present invention are: the present invention obtains nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material through a simple one-step solvothermal method, and the material can be applied in the field of photocatalysis. In the traditional laboratory preparation process, at least three steps of hydrothermal method are required to prepare the composite material, which saves nearly 48 hours of time. However, we adopted a one-step solvothermal scheme, and not only synthesized nitrogen-sulfur co-doped titania and nitrogen-sulfur co-doped graphene quantum dots, but also formed a heterojunction between them, which is more conducive to the improvement of catalytic performance. . In terms of morphology, through solvothermal action, more crystal faces of titanium dioxide (101) will be exposed, and titanium dioxide (101) has the highest activity, which will accelerate the catalytic process. In terms of band gap, the heterojunction formed by co-doping significantly reduces the band gap, which is 0.6eV lower than that of pure phase titanium dioxide, and can absorb visible light around 500nm. In terms of catalysis, the nitrogen-sulfur co-doped heterojunction exhibits excellent catalytic performance, and the maximum degradation efficiency can reach more than 90% in 120 minutes, which is significantly better than single nitrogen-sulfur-doped titanium dioxide and titanium dioxide-graphene quantum dot composites. . In terms of cycle stability, the nitrogen-sulfur co-doped heterojunction material has good stability. After 4 cycle experiments, the degradation efficiency loss is controlled at 2.57%, which is much smaller than the conventional 10% loss rate, and can be suitable for many recycle. In summary, the synthesis method has low cost of raw materials, simple steps, superior performance, high stability, and is suitable for mass production.

Description of drawings

Fig. 1 is the X-ray diffraction pattern (XRD) of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material prepared in Examples 1-3 of the present invention.

Fig. 2 is the scanning electron micrograph (SEM) of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material prepared in Example 2 of the present invention.

Fig. 3 is the transmission electron micrograph (TEM) of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material prepared in Example 2 of the present invention.

Fig. 4 is the X-ray photoelectron spectrum (XPS) of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material prepared in Example 2 of the present invention.

Fig. 5 is the ultraviolet-visible diffuse emission spectrogram (UV-bis) of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material prepared in Examples 1-3 of the present invention.

Fig. 6 is a diagram of visible light catalytic degradation dyes of nitrogen and sulfur co-doped titanium dioxide, nitrogen and sulfur co-doped graphene quantum dot composite materials prepared in Examples 1-3 of the present invention.

Fig. 7 is a graph of visible light catalytic degradation dye cycle efficiency of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material prepared in Example 2 of the present invention.

In the above figures, A is commercially available titanium dioxide powder (P25), and B prepares nitrogen for embodiment 1, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material NSTG (2:1), C is the NSTG (1:1) composite material prepared in Example 2, and D is the NSTG (1:3) composite material prepared in Example 3.

detailed description

Example 1:

Preparation of nitrogen, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material NSTG (2:1)

(1) According to the molar ratio of citric acid and thiourea being 2:1, weigh 0.42g of citric acid and 0.08g of thiourea.

(2) Add the powder weighed in step 1 into 8ml of dimethylformamide solution in sequence, and stir rapidly until it is completely dissolved.

(3) Weigh 100 mg of titanium dioxide (P25) powder, slowly add it into the solution obtained in step 2, and stir rapidly until it becomes a suspension.

(4) Transfer the suspension obtained in step 3 to a 40ml reaction kettle, and react at 180°C for 6 hours.

(5) Naturally cool to room temperature, remove the reaction kettle, and centrifuge the precipitate at 8500 rpm for 20 minutes to obtain a gray sample.

(6) The sample obtained in step 5 was washed twice with ethanol at 8500 rpm for 10 minutes, and the supernatant was discarded to obtain a sample.

(7) Wash the sample obtained in step 6 with ultrapure water twice, at 8500 rpm for 10 minutes, and pour off the supernatant to obtain a sample.

(8) The sample obtained in step 7 was vacuum-dried at 60° C. for 12 hours to obtain nitrogen, sulfur co-doped titanium dioxide, nitrogen, and sulfur co-doped graphene quantum dot composite material.

(9) Measure the methylene blue of 80ml, concentration 10mg/L, weigh 20mg of the sample prepared in step 8, join in the above-mentioned solution, under 100W, disperse ultrasonically for 30 minutes, place the beaker in a magnetic stirrer and stir, and Stir in a dark box for 30 minutes to irradiate the sample with a 300W xenon lamp, take out 4ml of the solution every 1 hour and place it in a 10ml centrifuge tube, centrifuge at 5000rpm for 5 minutes to precipitate the catalyst, remove the supernatant to a 5ml centrifuge tube for testing. After 4 hours of irradiation at visible wavelengths, the concentration of methylene blue in centrifuge tubes was measured using UV-bis. The measured photocatalytic degradation performance of the dye is shown in Figure 6.

(10) Recover the remaining samples of the photocatalytic reaction in step 9, wash and dry, continue to operate according to step 9, and cycle 3 times in sequence. The measured photocatalytic degradation efficiency changes are shown in Figure 7.

Example 2:

In Example 1, change step 1 to: according to the molar ratio of citric acid and thiourea being 1:1, weigh 0.42 g of citric acid and 0.15 g of thiourea. The rest of the steps are consistent with Example 1. Finally, the sample NSTG (1:1) was prepared. The photocatalytic degradation dye performance test process is the same as step 9 of Example 1.

Fig. 3 is the TEM figure of the sample prepared in embodiment 2, under low magnification, it can be seen that nitrogen-sulfur-doped titanium dioxide exists with nanoparticle morphology, and nitrogen-sulfur-doped graphene quantum dots are compact due to the small size (about 5nm) Tightly adhere to the surface of titanium dioxide to form a heterojunction. At high resolution, the exposed (101) crystal plane of titanium dioxide can be clearly seen. Due to the effect of heterojunction, the (1120) crystal plane of nitrogen-sulfur-doped graphene quantum dots is closely connected, and the two crystal planes cooperate The effect can speed up the catalytic process, so that the prepared samples have excellent catalytic performance.

Figure 7 is the cycle stability analysis diagram of the sample prepared in Example 2. It can be seen that the nitrogen-sulfur-doped titanium dioxide and nitrogen-sulfur-doped graphene quantum dot heterojunction undergo 4 cycles of degradation experiments, and the degradation efficiency loss is 2.57%. . The degradation efficiency loss of conventional single doped titanium dioxide or titanium dioxide-graphene quantum dot composite is about 10%. The sample prepared in Example 2 has very good cycle stability, which is also due to the relatively strong chemical bonding between the two under the action of the heterojunction.

Embodiment 3:

In Example 1, change step 1 to: according to the molar ratio of citric acid and thiourea being 1:3, weigh 0.42 g of citric acid and 0.46 g of thiourea. The rest of the steps are consistent with Example 1. Finally, the sample NSTG (1:3) was prepared. The photocatalytic degradation dye performance test process is the same as step 9 of Example 1.

Figure 4 is the N 1s and S 2p high-resolution characterization of the sample prepared in Example 2. Under N 1s high-resolution, 399.2, 399.7, 400.3, 401.3eV correspond to CNC, O-Ti-N, NH, Ti-ON bonds respectively Together, under the high resolution of S 2p, 163.6, 164.7, 168.3, and 169.6eV correspond to S 2p _3/2 , S 2p _1/2 , S=O, and SO bonding respectively. It is proved from the side that the sample prepared in Example 3 is Nitrogen-sulfur-doped titanium dioxide and nitrogen-sulfur-doped graphene quantum dots are heterojunctions, and there is a strong chemical bond between the heterojunctions, which is conducive to improving the stability of the material.

Fig. 5 is embodiment 1 (B), embodiment 2 (C) and embodiment 3 (D) product and the ultraviolet-visible diffuse reflectance spectrogram of P25 (A), as can be seen from the forbidden band width, embodiment 1, 2 , 3 The bandgap widths of B, C, and D prepared are 0.37, 0.60, and 0.48 eV lower than those of single titanium dioxide, which is conducive to better separation of electrons and holes and improved photocatalytic degradation performance.

Figure 6 is the degradation curves of B, C, D and P25 prepared in Example 2 and Example 3. It can be seen that the performance of sample C prepared in Example 2 is the best, and 90% degradation efficiency can be achieved in 120 minutes. The degradation efficiency of simple nitrogen-sulfur doped titanium dioxide and titanium dioxide-graphene quantum dot composites generally reaches about 50-60% in 120 minutes. Catalytic degradation performance.

As illustrated by the above examples, the preparation method of the composite material involved in the present invention has the advantages of simple operation, low cost, environmental friendliness, high repeatability, no secondary pollution, etc., and can obtain nitrogen and sulfur co-doped by a one-step solvothermal method A heterogeneous binary system. Visible by the curve D of accompanying drawing 6, the nitrogen prepared by the present invention, sulfur co-doped titanium dioxide, nitrogen, sulfur co-doped graphene quantum dot composite material, through photocatalytic degradation dye test, after dark box adsorption 30 minutes, degradation 4 hour, can be degraded completely, and the performance of its photocatalytic degradation dye is much higher than the performance (curve A of Fig. 6) of traditional titanium dioxide (P25), illustrates that the sample prepared by the present invention has very high catalytic activity. The final obtained solution is non-toxic, suitable for discharge of industrial waste water after cleaning, and reduces excessive energy consumption.

Claims (4)

1. a kind of nitrogen sulphur is co-doped with the one-step method for synthesizing of titanium dioxide/graphene quantum dot heterostructures, it is characterised in that including with Lower step：

(1) by citric acid and thiocarbamide according to mol ratio 2:1~1:3 are dissolved in dimethylformamide, and the concentration of citric acid is 12.5mol/L。

(2) during titanium dioxide (P25) adds the solution that step 1 is obtained, stirring obtains suspension, and the concentration of titanium dioxide is 15.6mol/L。

(3) suspension that step 2 is obtained is moved into reactor, and is reacted 6 hours at 180 DEG C, be centrifugally separating to obtain grey product Thing.

(4) gray product for obtaining will be reacted in step 3 respectively with after cleaning, vacuum drying finally gives nitrogen-sulphur codope two Titanium oxide/nitrogen-sulphur codope graphene quantum dot composite.

2. method according to claim 1, it is characterised in that the optimum molar ratio of citric acid and thiocarbamide in step 1 It is 1:1.

3. method according to claim 1, it is characterised in that step 3 centrifugation, rotating speed in 8000-9000rpm, when Between at 20-30 minutes.

4. method according to claim 1, it is characterised in that in the step 4, cleaned with ethanol and ultra-pure water respectively, It is each to clean twice, centrifugation, in 8000-9000rpm, centrifugation time was at 10-20 minutes for rotating speed.