CN108889329B - Carbon nitride quantum dot modified hierarchical pore TiO2-SiO2Photocatalyst and process for producing the same - Google Patents

Abstract

The invention relates to a TiO ₂ -SiO ₂ photocatalyst modified by carbon nitride quantum dots with a multi-level porous structure and a preparation method thereof. The main feature of the present invention is that carbon nitride quantum dots are introduced in the process of synthesizing ordered hierarchical porous TiO ₂ ‑SiO ₂ materials by an in-situ loading method, and carbon nitride quantum dots are obtained after the template agent is removed by a calcination method. Modified Hierarchical Porous Structured TiO ₂ ‑SiO ₂ Photocatalysts. Compared with the prior art, the method adopted in the present invention is simple and easy to operate, and can utilize the raw materials efficiently and can make the carbon nitride quantum dots supported in the pore walls of the hierarchical porous titanium oxide silicon oxide, thereby promoting the improvement of the photocatalytic activity, and at the same time. The ordered hierarchical pore structure also provides a good channel for the diffusion and transport of guest molecules, so that the prepared photocatalyst has good catalytic degradation activity against organic pollutants such as phenol and sulfadiazine, as well as the actual high-concentration antibiotic wastewater. .

Description

A kind of carbon nitride quantum dots modified hierarchical porous TiO2-SiO2 photocatalyst

technical field

The invention relates to the field of nanometer photocatalytic materials, and provides a novel photocatalyst and a preparation method thereof by supporting carbon nitride quantum dots in the pore walls of titanium oxide and silicon oxide with a hierarchical pore structure by in-situ loading.

Background technique

Mesoporous silica is a new type of nanomaterial developed in recent years. It has a specific surface area of up to 1000 m2/g, continuously adjustable pore size, highly long-range ordered channels, and high thermal stability. These excellent structural properties make them of great application value in catalysis, drug loading, exhaust gas adsorption, separation and purification, and solar-to-photoelectric conversion. Once reported, they have attracted extensive attention in various related fields. Especially in recent years, with the continuous innovation of synthesis technology, various structures such as KIT, MSU and SBA mesoporous silica have been reported, and the research on mesoporous materials has shown a booming scene. The research on mechanism and application has achieved fruitful results.

Photonic crystals (PCs) with ordered macroporous structures have become a research hotspot in recent years. Self-assembly of periodic "opal" templates can guide the infiltration and deposition of precursor materials to generate "inverse opals" (IOs) photonic crystal structures. The slow light effect and multi-light scattering effect of inverse opal photonic crystals can extend the optical path and increase the absorption of light, thereby improving the photocatalytic activity of the material. The photonic crystal structure and the mesoporous structure are combined to prepare a hierarchically porous silicon oxide material, which has the high specific surface area, high thermal stability and structural advantages of the mesoporous silicon oxide material as well as the photonic crystal material. However, due to the lack of catalytic activity of silica itself, the application of hierarchically porous silica materials in photocatalytic degradation of pollutants is limited. Titanium oxide is introduced into the hierarchical porous silica material to obtain a hierarchical porous TiO2-SiO2 photonic crystal photocatalyst, which has both the structural advantages of hierarchical pores and photocatalytic activity, and can effectively degrade pollutants. However, the forbidden band width of titanium oxide is 3.2 eV, corresponding to the absorption of ultraviolet light, and the visible light activity is insufficient.

Graphitic carbon nitride (g-C3N4), with a forbidden band width of 2.7 eV, is an excellent non-metallic semiconductor with chemical stability and is widely used in the degradation of organic pollutants. In recent years, graphitic carbon nitride quantum dots (CNQDs) have attracted extensive attention due to their strong blue light emission and upconversion behavior. Combining CNQDs with TiO2 in hierarchically porous titania and silica forms a Z framework, which improves the specific surface area, utilization of visible light, and charge transfer efficiency of the material, which is beneficial to the effective degradation of organic pollutants by photocatalysts.

There are few reports on the design of photocatalysts based on carbon nitride quantum dots, and there are basically no reports on the preparation of high-efficiency photocatalysts by combining carbon nitride quantum dots with hierarchically porous materials. Based on the above background, the present invention enables carbon nitride quantum dots to be supported in the pore walls of hierarchically porous titania-silica to promote the improvement of photocatalytic activity, and at the same time, the ordered hierarchical porous structure also provides good guest molecule diffusion and transport. The prepared photocatalyst has good catalytic degradation activity for organic pollutants such as phenol and sulfadiazine as well as actual antibiotic wastewater.

SUMMARY OF THE INVENTION

The invention adopts an in-situ loading method to prepare a carbon nitride quantum dot modified TiO2-SiO2 photocatalyst with a hierarchical porous structure in one step. In the process of preparing the composite photocatalyst, acetylacetone was added as a hydrolysis inhibitor of the titanium source to alleviate the excessive hydrolysis of the titanium source, and at the same time, the silicon source (tetrabutyl silicate), the prepared carbon nitride quantum dots and the titanium source were added. The source (isopropyl titanate) is poured into the polystyrene bead template, and the catalyst is easily synthesized by using the three to simultaneously hydrolyze on the micelle formed by the nonionic surfactant in the acidic system. High temperature calcination was used to remove the template, and carbon nitride quantum dots modified TiO2-SiO2 photocatalyst was obtained, which had good photocatalytic degradation effect on organic pollutants such as sulfadiazine and phenol and actual antibiotic wastewater.

The present invention is to prepare the above-mentioned photocatalyst, and the technological steps adopted are as follows:

The carbon nitride quantum dot solution was prepared by solid-phase hydrothermal method using sodium citrate and urea as raw materials; the pore-forming agent was dissolved in the ethanol solution, vigorously stirred for a certain period of time, and then the stirring speed was reduced, and tetrabutyl silicate was added , hydrochloric acid, acetylacetone, isopropyl titanate, carbon nitride quantum dot solution, obtained mixed solution, stirred, poured into polystyrene template, hydrolyzed and dried at a certain temperature and humidity for a certain period of time, and then in the air for a certain period of time The template is removed by calcination at a temperature for a certain period of time to obtain a TiO2-SiO2 photonic crystal photocatalyst modified by carbon nitride quantum dots with a hierarchical porous structure.

The reaction system is an acidic solution, which promotes the hydrolysis of ethyl orthosilicate while controlling the hydrolysis speed of isopropyl titanate, and avoids that the titanium cannot be monodispersed in the mesoporous framework due to the excessive hydrolysis of isopropyl titanate;

The concentration of the hydrochloric acid solution is 2mol/L-6mol/L; the pore-forming agent includes F127, P123, etc.; the stirring time is 0.5-2h; the hydrolysis temperature is 30°C-60°C, and the humidity is 40-60%; the calcination temperature is 400-600° C.; the calcination time is 2h-6h.

The advantages of the present invention are reflected in:

1) In the method of the present invention, the pore-forming agent and the template agent are hydrolyzed and dried at a certain temperature and humidity, and their combined action obtains a hierarchical pore structure with ordered mesoporous channels and inverse opal structures at the same time, so that titanium oxide and dialysis The obtained carbon nitride quantum dots are compounded in the framework of the hierarchical pores, and the three have a synergistic effect to improve the photocatalytic activity;

2) The simultaneous introduction of carbon nitride quantum dots and titanium can enable them to interact and co-dope in the pore walls of hierarchical porous silicon oxide, and ensure orderly and smooth channels and high specific surface area;

3) The ordered mesoporous channels and inverse opal structure provide a good channel for the diffusion and transport of guest molecules, which is also conducive to the improvement of photocatalytic activity;

4) The prepared carbon nitride quantum dots modified hierarchical porous structure TiO2-SiO2 photocatalyst has good catalytic degradation activity to organic pollutants such as sulfadiazine, phenol and high-concentration actual antibiotic wastewater;

5) The carbon nitride quantum dots have a synergistic effect with the hierarchical pore structure to promote the improvement of photocatalytic activity;

6) Compared with the traditional modification methods such as doping and compounding, the in-situ synthesis method is simple in equipment, convenient in operation, and can efficiently utilize raw materials, greatly reducing production costs and facilitating industrialization.

Description of drawings

Figure 1. (a) Me-TSCN-IO, (b) Me-TS-IO, (c) Me-TSCN, (d) Me-TS, (e) TSCN-IO, (f) TS-IO, ( g) SEM images of bulk-TSCN, (h) bulk-TS.

Figure 2. (a) Me-TSCN-IO, (b) Me-TS-IO, (c) Me-TSCN, (d) Me-TS, (e) TSCN-IO, (f) TS-IO, ( g) TEM images of bulk-TSCN, (h) bulk-TS.

Figure 3. HRTEM photograph of Me-TSCN-IO.

Figure 4. XRD patterns of carbon nitride quantum dots modified hierarchically porous TiO2-SiO2 photonic crystal photocatalyst (Me-TSCN-IO).

Figure 5. (a) nitrogen adsorption and desorption isotherms (b) pore size distribution curves of the samples.

Figure 6. Impedance plot of the sample.

Figure 7. Degradation activity of Me-TSCN-IO to 10 mg/L (a) phenol (b) sulfadiazine under 300W xenon lamp with AM1.5 filter.

Figure 8. Degradation activity graph of Me-TSCN-IO on actual antibiotic wastewater.

Figure 9. Cyclic stability plot of sample Me-TSCN-IO for photocatalytic degradation of (a) phenol (b) sulfadiazine.

Detailed ways

The present invention will be described in more detail below through specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

Preparation of carbon nitride quantum dots (CNQDs):

Using urea and sodium citrate as precursors, a low-temperature solid hydrothermal method is used to prepare water-phase carbon nitride quantum dots after dialysis treatment. Specifically, 0.081 g of sodium citrate and 0.101 g of urea were ground and mixed uniformly, and then transferred to the lining of the polytetrafluoroethylene reactor. Tightly seal the stainless steel jacket and keep it in an electric heating constant temperature blast drying oven at 180°C for 2h. After taking out the autoclave, it was naturally cooled at room temperature, and the brown solid was ultrasonically washed with absolute ethanol for three times, then put into a MWCO3500 dialysis bag, and dialyzed in 20 mL of deionized water for 24 hours at room temperature to obtain yellowish carbon nitride quantum dots. aqueous solution.

Example 1

To synthesize Me-TSCN-IO, carbon nitride quantum dots, pore-forming agents such as P123, tetrabutyl silicate and isopropyl titanate are added at the same time in the preparation process, and polystyrene is used as a template, and the specifics are:

After adding 30mL EtOH to the 50mL beaker, add 2g P123 and stir for 30min until it is completely dissolved. In the clear solution, 0.89 mL of tetrabutyl silicate (TEOS), 1 mL of HCl (4 mol/L), 1 mL of inhibitor acetylacetone, 4.8 mL of isopropyl titanate (TTIP) and 5 mL of CNQDs aqueous solution were added. After stirring for 2 h at room temperature, the precursor solution was perfused into the 355 nm PS template. The constant temperature and humidity box was hydrolyzed for 3 days at a temperature of 40 °C and a humidity of 55%, then transferred to a 70 °C oven for drying for 3 days, and calcined in a muffle furnace at 500 °C for 4 hours under an air atmosphere (heating rate 1 °C/min), so that the titanium oxide and The carbon nitride quantum dots are compounded in the framework, that is, a hierarchical porous titanium oxide silicon oxide composite photocatalyst modified by the carbon nitride quantum dots is obtained.

Comparative Example 1

To synthesize Me-TS-IO, only pore-forming agents such as P123, tetrabutyl silicate and isopropyl titanate are added in the preparation process, that is, the addition amount of carbon nitride quantum dots is 0, and polystyrene is used as a template:

After adding 30mL EtOH to the 50mL beaker, add 2g P123 and stir for 30min until it is completely dissolved. To the clear solution was added 0.89 mL of tetrabutyl silicate (TEOS), 1 mL of HCl, 1 mL of inhibitor acetylacetone, 4.8 mL of isopropyl titanate (TTIP) and 5 mL of deionized water. After stirring for 2 h at room temperature, the precursor solution was poured into the 355 nm PS template. The constant temperature and humidity box was hydrolyzed for 3 days at a temperature of 40 °C and a humidity of 55%, then transferred to a 70 °C oven for drying for 3 days, and calcined in a muffle furnace at 500 °C for 4 hours in an air atmosphere (heating rate of 1 °C/min) to obtain a multi-stage Porous titanium oxide silicon oxide composite photocatalyst.

Comparative Example 2

To synthesize Me-TSCN, carbon nitride quantum dots were added during the preparation process, pore-forming agents such as P123, tetrabutyl silicate and isopropyl titanate, and no polystyrene beads were used as templates:

After adding 30mL EtOH to the 50mL beaker, add 2g P123 and stir for 30min until it is completely dissolved. Add 0.89 mL of tetrabutyl silicate (TEOS), 1 mL of HCl, 1 mL of inhibitor acetylacetone, 4.8 mL of isopropyl titanate (TTIP) and 5 mL of CNQDs aqueous solution to the transparent solution, stir at room temperature for 2 hours, and then put it into constant temperature and humidity. After hydrolysis for 3 days at a temperature of 40 °C and a humidity of 55% in the box, it is transferred to a 70 °C oven for drying for 3 days, and calcined in a muffle furnace at 500 °C for 4 hours in an air atmosphere (heating rate of 1 °C/min) to obtain carbon nitride quantum Dot-modified mesoporous titania-silica composite photocatalysts.

Comparative Example 3

To synthesize TSCN-IO, only carbon nitride quantum dots, tetrabutyl silicate and isopropyl titanate were added in the preparation process, that is, when the amount of pore-forming agent such as P123 was 0, polystyrene beads were used as templates The resulting catalyst:

After adding 30 mL of EtOH to a 50 mL beaker, stir for 30 min until completely dissolved. To the clear solution were added 0.89 mL of tetrabutyl silicate (TEOS), 1 mL of HCl, 1 mL of inhibitor acetylacetone, 4.8 mL of isopropyl titanate (TTIP) and 5 mL of CNQDs aqueous solution. After stirring for 2 h at room temperature, the precursor solution was poured into the 355 nm PS template. The constant temperature and humidity box was hydrolyzed for 3 days at a temperature of 40 °C and a humidity of 55%, then transferred to a 70 °C oven for drying for 3 days, and calcined in a muffle furnace at 500 °C for 4 hours under an air atmosphere (heating rate 1 °C/min), so that the titanium oxide and The carbon nitride quantum dots are compounded in the framework, that is, the carbon nitride quantum dots modified macroporous structure titanium oxide silicon oxide composite photocatalyst is obtained.

Comparative Example 4

To synthesize bulk-TS, only tetrabutyl silicate and isopropyl titanate are added in the preparation process, that is, when the addition amount of pore-forming agents such as P123 and carbon nitride quantum dots is 0, no polystyrene beads are used as Template obtained catalyst:

Add 30 mL absolute ethanol, 0.89 mL tetrabutyl silicate (TEOS), 1 mL HCl, 1 mL inhibitor acetylacetone, 4.8 mL isopropyl titanate (TTIP) and 5 mL deionized water to a 50 mL beaker, and stir at room temperature for 2 h Then put it into a constant temperature and humidity box to hydrolyze for 3 days at a temperature of 40 °C and a humidity of 55%, then transfer it to a 70 °C oven for drying for 3 days, and calcinate it in a muffle furnace at 500 °C for 4 hours in an air atmosphere (heating rate 1 °C/min), That is, a bulk titanium oxide silicon oxide composite photocatalyst is obtained.

Experiments and Data

The method for investigating the activity of photocatalytic degradation of simulated pollutants provided by the present invention is as follows:

Take 50 mg of composite photocatalyst, put it into a quartz glass tube, and add 50 mL of 10 mg/L target organic pollutant solution. Under magnetic stirring, the catalyst is pre-adsorbed to the organic matter for 30 min to reach the adsorption-desorption equilibrium. Degradation initial concentration. Then carry out photocatalytic degradation of organic pollutants under a 300W xenon lamp, take samples at regular intervals and place them in a centrifuge tube for centrifugation, take the supernatant and filter the catalyst with a filter head. If the target is to simulate organic waste water such as phenol and sulfadiazine, pass High performance liquid chromatography is used to test the amount of degradation. If the target is actual wastewater such as the actual wastewater of antibiotics from North China Pharmaceutical Group Co., Ltd., the COD analyzer and TOC analyzer are used to test the chemical oxygen demand (COD) and total organic carbon (TOC), and then cartographic analysis.

FIG. 1 is a scanning electron microscope (SEM) photograph of the samples obtained in Example 1 and Comparative Examples 1-4. From the SEM photos, it can be seen that carbon nitride quantum dots modified hierarchical porous TiO2-SiO2 photonic crystal (Me-TSCN-IO), hierarchical porous TiO2-SiO2 photonic crystal (Me-TS-IO), nitrided Carbon quantum dots modified macroporous structure TiO2-SiO2 photonic crystal (TSCN-IO) has obvious inverse opal macroporous structure, carbon nitride quantum dots modified mesoporous structure TiO2-SiO2 (Me-TSCN) and ordinary TiO2-SiO2 (bulk-TS) does not have a regular macroporous structure.

2 is a transmission electron microscope (TEM) photograph of the samples obtained in Example 1 and Comparative Examples 1-4. From the TEM images, it can be seen that Me-TSCN-IO, Me-TS-IO, and TSCN-IO have obvious inverse opal macroporous structures, while Me-TSCN and bulk-TS do not have regular macroporous structures.

3 is a high-power transmission electron microscope (HRTEM) photograph of the Me-TSCN-IO sample obtained in Example 1. A clear mesoporous structure and an inverse opal structure can be seen from the HRTEM images, proving the formation of a hierarchical pore structure, and different lattice fringes can be observed, corresponding to the (002) plane and the (100) plane of carbon nitride, respectively. ) plane and the (101) plane of titanium oxide, demonstrating the successful loading of carbon nitride quantum dots.

FIG. 4 is the XRD patterns of the samples obtained in Example 1 and Comparative Examples 1-4. On the wide-angle XRD spectrum, the peak of titanium oxide can be observed, and the peak of carbon nitride is not observed because the amount of carbon nitride is too small.

Figure 5 is a graph showing the nitrogen adsorption and desorption isotherms and pore size distribution curves of samples prepared in Example 1 and Comparative Examples 2-3. From the nitrogen adsorption and desorption isotherm, it can be seen that Me-TSCN-IO has both the hysteresis loops of macroporous material TSCN-IO and mesoporous material Me-TSCN, indicating that Me-TSCN-IO has a hierarchical pore structure. From the pore size distribution curve, it can be explained that the introduction of mesopores makes Me-TSCN-IO have a larger pore volume than the macroporous material TSCN-IO.

6 is an impedance diagram of the samples obtained in Example 1 and Comparative Examples 1-3. It can be seen from the figure that the carbon nitride quantum dot-modified hierarchically porous titania-silicon oxide photonic crystal has the smallest impedance radius, indicating that the loading of carbon nitride quantum dots promotes the separation of photogenerated electrons and holes.

Figure 7 is a graph showing the degradation activity of the photocatalysts obtained in Example 1 and Comparative Examples 1-4 to 10 mg/L phenol and sulfadiazine under a 300W xenon lamp equipped with an AM1.5 filter. For the degradation of both phenol and sulfadiazine, the catalytic activity of the carbon nitride quantum dot-modified hierarchical porous TiO2-SiO2 photonic crystal Me-TSCN-IO is higher than that of the non-carbon nitride quantum dot modified hierarchical porous TiO2-SiO2 Photonic crystal Me-TS-IO has more excellent photocatalytic activity, which proves that the loading of carbon nitride quantum dots contributes to the improvement of photocatalytic activity; Crystal Me-TSCN-IO ratio Mesoporous carbon nitride quantum dots modified TiO2-SiO2 material Me-TSCN, simple macroporous carbon nitride quantum dots modified TiO2-SiO2 photonic crystal TSCN-IO and bulk TiO2 -SiO2 material bulk-TS catalyst has good effect, which proves that the hierarchical pore structure has more advantages than pure mesopore and macroporous structure. In summary, the synergistic effect of carbon nitride quantum dots and hierarchical pore structure enhances the photocatalytic activity of the material for the degradation of organic pollutants such as phenol and sulfadiazine.

8 is a graph showing the degradation activity of the photocatalyst obtained in Example 1 on the actual wastewater of high-concentration antibiotics of North China Pharmaceutical Group Co., Ltd. (Shijiazhuang, Hebei) under a 300W xenon lamp with an AM1.5 filter added. It can be seen from the figure that with the progress of illumination, the COD and TOC values of the actual wastewater with high concentrations of antibiotics gradually decreased. TOC=63750 mg/L). It shows that the prepared catalyst has a good photocatalytic degradation effect on the actual high-concentration antibiotic wastewater.

Fig. 9 is a cycle stability diagram of the photocatalyst obtained in Example 1 for photocatalytic degradation of phenol and sulfadiazine under a 300W xenon lamp equipped with an AM1.5 filter. It can be seen from the figure that after five cycles of experiments, the photocatalytic degradation effect of the catalyst on phenol and sulfadiazine does not significantly decrease, indicating that the catalyst has good stability and can be reused.

While the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be construed as limiting the present invention.

Claims (6)

1. a method for preparing carbon nitride quantum dots modified hierarchical porous structure TiO ₂ -SiO ₂ photonic crystal photocatalyst, it is characterized in that, the carbon nitride quantum dots of described catalyst are doped in hierarchical porous titanium oxide oxidation In the skeleton of the silicon photonic crystal, the specific experimental steps are as follows: 1), the sodium citrate and urea are ground and mixed and transferred to the lining of the polytetrafluoroethylene reactor, kept at 160-200 ° C for a certain period of time, cooled, and the brown solid obtained is separated, and then ultrasonically washed with absolute ethanol After three times, put it into a dialysis bag, and dialyze it in deionized water for a certain period of time at room temperature to obtain a yellowish carbon nitride quantum dot aqueous solution; 2), after adding EtOH in the container, then add P123, stir until completely dissolved to obtain a transparent solution, add tetrabutyl silicate (TEOS), hydrochloric acid, acetylacetone, isopropyl titanate (TTIP) and Carbon nitride quantum dot aqueous solution, stirred at room temperature, poured the precursor solution into the PS template of 300-400nm, hydrolyzed at a predetermined temperature and humidity for a predetermined time, transferred to an oven to dry, and calcined in a muffle furnace in an air atmosphere , so that the titanium oxide and carbon nitride quantum dots are compounded in the framework, that is, a hierarchical porous titanium oxide silicon oxide photocatalyst modified by carbon nitride quantum dots is obtained. 2. method according to claim 1 is characterized in that: the concentration of described hydrochloric acid is 2mol/L-6mol/L. 3. The method of claim 1, wherein the stirring time is 0.5-2h. 4. The method of claim 1, wherein the temperature of the hydrolysis is 30-60°C, and the humidity is 40-60%. 5. The method according to any one of claims 1-4, wherein the calcining temperature is 400-600°C; the calcining time is 2-6h. 6. A carbon nitride quantum dot modified hierarchical porous structure TiO ₂ -SiO ₂ photonic crystal photocatalyst, characterized in that the carbon nitride quantum dots of the catalyst are doped in the hierarchical porous titanium oxide silicon oxide photonic crystal In the framework of , the catalyst is prepared by the method described in any one of claims 1-5.

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