CN109985651A - A kind of graphitic carbon nitride/silver oxide composite photocatalyst and preparation method thereof - Google Patents

Abstract

A kind of graphite phase carbon nitride/silver oxide composite photo-catalyst and preparation method thereof, graphite phase carbon nitride/silver oxide composite photo-catalyst preparation method include the following steps: 1) to calcine dicyanodiamine at 450-650 DEG C and obtain g-C₃N₄；2) g-C is prepared₃N₄Dispersion liquid, to g-C₃N₄Sodium hydroxide is added in dispersion liquid and silver nitrate is reacted, obtains crude product, crude product is washed, is dried to obtain Ag₂O/g‑C₃N₄Composite photo-catalyst.The Ag being prepared according to the method for the present invention₂O/g‑C₃N₄Composite photo-catalyst has good photocatalytic activity and stability.

Description

A kind of graphitic carbon nitride/silver oxide composite photocatalyst and preparation method thereof

technical field

The invention belongs to the technical field of photocatalysis, and in particular relates to a graphite phase carbon nitride/silver oxide composite photocatalyst and a preparation method thereof.

Background technique

Solar energy is a kind of renewable and clean energy. With the depletion of fossil fuels, solar energy has gradually become an important part of human energy. Under the trend of sustainable development, photocatalytic technology has been proved to be an efficient, green and promising emerging technology. Photocatalysis technology is a technology based on the special energy band structure of semiconductors, the core of which is semiconductor photocatalysts. However, the researchers found that the photocatalyst currently studied is _{TiO 2} , which has a wide band gap (3.2 eV), can only absorb ultraviolet light less than 387 nm, has low solar energy utilization, and has a high carrier recombination rate. The catalytic efficiency is low. The solar spectrum consists of 5% ultraviolet light, 42-45% visible light, and more than 50% near-infrared (NIR) light. However, most of the photocatalysts currently studied only absorb ultraviolet light, or absorb a part of visible light, which is very harmful to sunlight. The utilization rate is low, thus limiting its large-scale practical application. In order to make full use of solar energy, it is of great practical significance to develop novel photocatalysts with excellent near-infrared light response.

SUMMARY OF THE INVENTION

The technical problem solved by the present invention is: the present invention adopts a common chemical synthesis method to prepare a semiconductor material graphite phase carbon nitride (gC ₃ N ₄ ) and a metal compound photocatalyst silver oxide (Ag ₂ O) composite photocatalyst Ag ₂ O /gC ₃ N ₄ , has good photocatalytic activity under near-infrared light, and improves the utilization efficiency of sunlight.

The specific solution provided by the present invention includes the following steps:

1) calcining dicyandiamide at 450-650° C. to obtain gC ₃ N ₄ ;

2) prepare gC ₃ N ₄ dispersion, add sodium hydroxide and silver salt to the gC ₃ N ₄ dispersion to react to obtain a crude product, wash and dry the crude product to obtain Ag ₂ O/gC ₃ N ₄ composite photocatalyst.

Beneficial effects:

Silver oxide Ag ₂ O is a non-toxic and harmless brown powder with a simple cubic structure, which is the most thermodynamically stable silver oxide. As a p-type semiconductor, silver oxide was found to be a visible photocatalyst with a narrow 1.2ev energy bandgap, its valence band is about 1.4ev and its conduction band is about 0.2ev, and silver oxide has excellent visible-to-near-infrared light However, due to its narrow band gap and high electron and hole recombination rates, pure Ag ₂ O is greatly limited in photocatalytic applications. _gC3N4 is an inorganic semiconductor material with a typical semiconductor energy band structure, its valence band is about _1.4eV , conduction band is about -1.30eV, and forbidden band width is about 2.7eV. It is a kind of visible light responsive photocatalytic materials.

Due to the difference in Fermi level and energy band position between _Ag2O and _gC3N4 , _Ag2O and _gC3N4 in _{Ag2O / gC3N4} form a _{pn heterostructure} , and in the pn heterostructure The mass-junction interface forms an internal electric field. Under the irradiation of near-infrared light, only silver oxide Ag ₂ O can be excited to generate electrons and holes, and electrons (e ^- ) in the valence band (VB) of Ag ₂ O can be excited to the conduction band CB. The same amount of holes (h ⁺ ) is left on the band. Meanwhile, the photogenerated electrons on the conduction band CB of Ag ₂ O will be transferred to the conduction band CB of the corrected gC ₃ N ₄ under the action of the internal electric field, which helps Due to the separation of photogenerated electrons and holes of Ag ₂ O, the recombination of electrons and holes in Ag ₂ O is greatly reduced, and the photocatalytic activity of Ag ₂ O is effectively improved.

On the basis of above-mentioned technical scheme, the present invention can also do following improvement:

Further, the calcination time of step 1) is 2-6h.

Under this condition, dicyandiamide can fully react to obtain gC ₃ N ₄ with high yield and high purity.

Specifically, in an air atmosphere, the muffle furnace was heated to 450-650° C. and calcined for 2-6 hours, then cooled to room temperature naturally, and ground to obtain a pale yellow solid product.

Further, the heating rate in step 1) is 0.5-3°C/min.

Specifically, in step 1), in an air atmosphere, the temperature in the muffle furnace is heated to 450-650° C. at a heating rate of 0.5-3° C./min.

Preferably, in step 1), the heating rate is 1-2 °C/min.

Under this condition, gC ₃ N ₄ is obtained in high yield and high crystallinity.

Further, the dispersing solvent of the gC ₃ N ₄ dispersion in the step 2) is pure water, and the concentration of gC ₃ N ₄ in the dispersion is 0.18-1.2 g/L.

Thus, only a small amount of gC ₃ N ₄ needs to be added to obtain an Ag ₂ O/gC ₃ N ₄ composite photocatalyst with high photocatalytic activity.

Further, in step 2), gC ₃ N ₄ is added to pure water for 20-40 min to be sonicated to obtain a gC ₃ N ₄ dispersion.

Under this condition, gC ₃ N 4 in gC ₃ N ₄ dispersion liquid is uniformly dispersed.

Further, in step 2), the mass ratio of gC ₃ N ₄ to the silver salt is 1:(6-40).

Further, the concentration of sodium hydroxide in the gC ₃ N ₄ dispersion after adding sodium hydroxide and silver nitrate in step 2) is 0.1-0.5 mol/L.

Preferably, the concentration of sodium hydroxide in the gC ₃ N ₄ dispersion after adding sodium hydroxide and silver nitrate in step 2) is 0.1-0.5 mol/L.

Under this condition, high yield and high activity Ag ₂ O/gC ₃ N ₄ composite photocatalyst can be obtained.

Further, in step 2), the gC ₃ N ₄ dispersion after adding sodium hydroxide and silver nitrate is continuously stirred for 20-40 min to obtain the crude product.

Under this condition, the raw materials can be fully reacted, and the composite photocatalyst has good photocatalytic activity.

Further, step 2) is performed in a dark room.

This can prevent the silver nitrate solution from decomposing under the light to generate Ag, and thus, gC ₃ N ₄ /Ag ₂ O with high purity can be obtained.

The Ag ₂ O/gC ₃ N ₄ composite photocatalyst prepared according to the method of the invention has good photocatalytic activity under near-infrared light and improves the utilization efficiency of sunlight; the Ag ₂ O/gC ₃ N ₄ composite catalyst By improving the separation rate of photogenerated electrons and holes of Ag ₂ O, its photocatalytic activity is obviously better than that of pure Ag ₂ O photocatalyst.

The present invention also provides a graphitic carbon nitride/silver oxide composite photocatalyst, which is prepared according to the above-mentioned graphitic carbon nitride/silver oxide composite photocatalytic preparation method.

Thus, the gC ₃ N ₄ /Ag ₂ O composite photocatalyst has good photocatalytic activity and stability.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

Figure 1 shows the photocatalytic degradation of RhB by gC ₃ N ₄ /Ag ₂ O composite photocatalyst in the near-infrared region.

Figure 2 is a graph showing the spectral changes of the gC ₃ N ₄ /Ag ₂ O (1:16) composite photocatalyst in the degradation of RhB in the near-infrared region.

Figure 3 is a graph of the cyclic degradation of the gC ₃ N ₄ /Ag ₂ O (1:16) composite photocatalyst in the near-infrared region.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

The present invention is described below in conjunction with Figures 1-3 and with reference to specific embodiments.

Example 1

(1) Preparation of gC ₃ N ₄

Take 2g of solid dicyandiamide and put it into a crucible with a lid. Under the air atmosphere, in a muffle furnace, the temperature is raised to 450°C at a heating rate of 0.5°C/min and calcined for 2h, and then naturally cooled to room temperature. Yellow _gC3N4 solid powder _.

(2) Preparation of Ag ₂ O/gC ₃ N ₄ composite photocatalyst

Add 0.0368 g gC ₃ N ₄ powder to 30 ml of deionized water and sonicate for 30 min to obtain a gC ₃ N ₄ dispersion, add 0.17 g NaOH to the gC ₃ N ₄ dispersion and stir for 30 min, add dropwise with stirring 13mL of 0.1mol/L AgNO ₃ solution was reacted. In the dark, stirring was continued for 20 minutes. The crude product was obtained by centrifugation with a centrifuge, and then washed with deionized water and centrifuged for three times. The solid product was dried at 60°C for 12h. .

Example 2

(1) Preparation of gC ₃ N ₄

Take 12g of solid dicyandiamide and put it into a covered crucible. Under the air atmosphere, in a muffle furnace, the temperature is raised to 650°C at a heating rate of 3°C/min and calcined for 6h, and then naturally cooled to room temperature. Yellow _gC3N4 solid powder _.

(2) Preparation of Ag ₂ O/gC ₃ N ₄ composite photocatalyst

0.0055 g of gC ₃ N4 powder was added to 30 ml of deionized water and sonicated for 30 min to obtain a gC ₃ N ₄ dispersion. 0.86 g of NaOH was added to the gC _{3 N4} dispersion and stirred for 30 min. Under stirring conditions, 13 mL of .1mol/L AgNO ₃ solution was reacted, stirring was continued for 40 minutes under dark conditions, and the crude product was obtained by centrifugation with a centrifuge, washed with deionized water and centrifuged, repeated three times, and the solid product was dried at 60 °C for 12 h.

Example 3

(1) Preparation of gC ₃ N ₄

Take 5g of solid dicyandiamide and put it into a covered crucible. Under the air atmosphere, in a muffle furnace, the temperature is raised to 550°C at a heating rate of 1.5°C/min and calcined for 4h, and then cooled to room temperature naturally. Yellow _gC3N4 solid powder _.

(2) Preparation of Ag ₂ O/gC ₃ N ₄ composite photocatalyst

0.0188 g of _gC3N4 powder was added to 30 ml of deionized water and sonicated for ₃₀ min to obtain a _gC3N4 dispersion, 0.6 g NaOH was added to the _{gC3N4 dispersion} and stirred for ₃₀ min, and added dropwise under stirring conditions 13mL of 0.1mol/L AgNO ₃ solution was reacted, and continued stirring for 30 minutes under dark conditions, and the crude product was obtained by centrifugation with a centrifuge, washed with deionized water and centrifuged, repeated three times, and the solid product was dried at 60 ° C. 12h.

Examples 4-6

Similar to Example 1, the difference is that the amount of gC ₃ N ₄ taken in Example 4, Example 5 and Example 6 is 0.0368g, 0.0094g and 0.0047g, respectively.

Comparative Example 1

Take 5g of solid dicyandiamide and put it into a covered crucible. Under the air atmosphere, in a muffle furnace, the temperature is raised to 550°C at a heating rate of 1.5°C/min and calcined for 4h, and then cooled to room temperature naturally. Yellow _gC3N4 solid powder _.

Comparative Example 2

0.6g NaOH was added to pure water and stirred for 30min. Under stirring conditions, 13mL of 0.1mol/L AgNO ₃ solution was added dropwise to obtain a mixed reaction solution, and the mixed reaction solution was continuously stirred for 30 minutes under dark conditions. The crude product was obtained by centrifugation in a centrifuge, washed with deionized water and centrifuged, repeated three times, and the solid product was dried at 60° C. for 12 h to obtain Ag ₂ O.

Photocatalytic activity analysis of catalysts

Activity tests were performed on the final products in Examples 3-6 and Comparative Examples 1-2, respectively, and two groups of control experiments were performed. Take 100 mL of 10 mg/L Rhodamine B (RhB) solution, the dosage of photocatalyst is 0.1 g, and after uniform dispersion, take 6 mL of RhB stock solution and mark it as the No. 1 sample. In the absence of light, stir for 30 min to make the catalyst reach adsorption-desorption equilibrium in the RhB solution, draw 6 mL of the reaction solution and mark it as sample No. 2, turn on the light source (light source wavelength λ≥800 nm) and start timing, the mixed reaction solution is in Degradation was carried out under visible light for 120 min, samples were taken every 30 min, the samples were centrifuged in a centrifuge for 10 min, 5 mL of supernatant was taken and the absorbance value was measured on a full-scan UV-Vis spectrophotometer, and the target pollutant solution was recorded. Absorbance value at the wavelength of maximum absorption (ie, at 554 nm).

The photocatalytic degradation effect of the catalyst material on RhB was analyzed by detecting the absorbance of the solution under different illumination times, as shown in formula (1):

Among them, C ₀ and A ₀ represent the initial concentration and absorbance value of the solution, respectively, and C _t and A _t represent the solution concentration and absorbance after the illumination time th, respectively.

The results are shown in Figure 1. In the case of no light and photocatalyst (control 1), RhB is almost not degraded; in the case of no catalyst and only near-infrared light (control 2), RhB is also almost not degraded. It can be shown that the photocatalytic degradation of RhB by gC ₃ N ₄ /Ag ₂ O composite photocatalyst in the near-infrared region is completed under the combined action of light and photocatalyst; pure gC ₃ N ₄ has almost no effect on RhB in the near-infrared region. Produce photocatalytic degradation, pure Ag ₂ O has photocatalytic degradation effect on RhB in the near-infrared region, but compared with pure gC ₃ N ₄ and Ag ₂ O, the gC ₃ N ₄ /Ag ₂ O composite photocatalyst has a photocatalytic degradation in the near-infrared region. The photocatalytic performance of the light region is obviously enhanced; in the synthesis process of the photocatalyst, when the added amount of gC ₃ N ₄ is 0.0368g, 0.188g, 0.0094g and 0.0047g, respectively, that is, the mass of gC ₃ N ₄ /Ag ₂ O The ratios are respectively 1:8 (Example 4), 1:16 (Example 3), 1:32 (Example ₅ ), 1:64 (Example ₆ ), and the obtained _gC3N4 /Ag2O composite The photocatalyst activity was significantly higher than that of pure Ag ₂ O photocatalyst, and the removal rates of RhB were 57%, 61%, 56% and 40%, respectively, after 5 hours of illumination. In the process of changing the mass ratio of gC ₃ N ₄ /Ag ₂ O from 1:8 to 1:64, the activity of the obtained composite photocatalyst first increased and then decreased. When the mass ratio of gC ₃ N ₄ /Ag ₂ O is 1:16, the obtained composite catalyst has the highest photocatalytic activity. As shown in Figure 2, the spectral changes of the gC ₃ N ₄ /Ag ₂ O (1:16) composite photocatalyst in the near-infrared region of RhB degradation, with the increase of the reaction time, the maximum absorption peak of RhB at 554nm absorbance value It gradually decreased and was close to 0 after 5h, indicating that RhB molecules were effectively decomposed. When the mass ratio of the composite photocatalyst is 1:64, the catalytic performance is similar to that of pure Ag ₂ O. This may be because the proportion of gC ₃ N ₄ only accounts for 1.5% of the composite photocatalyst, and the content of gC ₃ N ₄ is too small, so it is similar to pure Ag 2 O. There is little difference in the activity of Ag ₂ O.

Using the thiocyanic acid gC ₃ N ₄ /Ag ₂ O (1:16) prepared in Example 1 as the catalyst, the photocatalytic (light source wavelength λ≥800nm) degradation of RhB was carried out in a cycle experiment, as shown in Figure 3, after 4 cycles , gC ₃ N ₄ /Ag ₂ O still has good photocatalytic activity, indicating that the gC ₃ N ₄ /Ag ₂ O catalyst prepared by this method has good photocatalytic stability.

Although the embodiments of the present invention have been described in detail above, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the invention is defined by the claims and their equivalents.

Claims (10)

1. a graphite phase carbon nitride/silver oxide composite photocatalyst preparation method, is characterized in that, comprises the steps: 1) calcining dicyandiamide at 450-650° C. to obtain gC ₃ N ₄ ; 2) prepare gC ₃ N ₄ dispersion, add sodium hydroxide and silver nitrate to the gC ₃ N ₄ dispersion to react to obtain a crude product, wash and dry the crude product to obtain Ag ₂ O/gC ₃ N ₄ composite photocatalyst. 2. The method for preparing graphitic carbon nitride/silver oxide composite photocatalysis according to claim 1, wherein the calcination time in step 1) is 2-6h. 3 . The method for preparing graphitic carbon nitride/silver oxide composite photocatalysis according to claim 1 , wherein the heating rate in step 1) is 0.5-3° C./min. 4 . 4. The method for preparing graphitic carbon nitride/silver oxide composite photocatalysis according to claim 1, wherein in step ₂ ), the dispersing solvent of _gC3N4 dispersion liquid is pure water, and gC3N4 in the dispersion liquid is pure water. The concentration of ₃ N ₄ is 0.18-1.2 g/L. 5. The method for preparing graphitic carbon nitride/silver oxide composite photocatalysis according to claim 4, characterized in that, in step 2), gC ₃ N ₄ is added to pure water for 20-40 min of ultrasonic wave to obtain gC ₃ N ₄ dispersions. 6. The graphitic carbon nitride/silver oxide composite photocatalytic preparation method according to claim 1, wherein in step 2), the mass ratio of _gC3N4 to the silver nitrate is ₁ : (6-40 ). 7. The graphitic carbon nitride/silver oxide composite photocatalytic preparation method according to claim 1, wherein in step ₂ ), sodium hydroxide in the _gC3N4 dispersion liquid after adding sodium hydroxide and silver nitrate The concentration is 0.1-0.5mol/L. 8. The graphitic carbon nitride/silver oxide composite photocatalytic preparation method according to claim 1, wherein in step ₂ ), the _gC3N4 dispersion liquid after adding sodium hydroxide and silver nitrate is continued Stir for 20-40 min to obtain the crude product. 9. The method for preparing graphitic carbon nitride/silver oxide composite photocatalysis according to any one of claims 1-8, wherein step 2) is performed in a dark room. 10. A graphitic carbon nitride/silver oxide composite photocatalyst, characterized in that it is prepared by the graphitic carbon nitride/silver oxide composite photocatalytic preparation method described in any one of claims 1-9.