Visible-light response hybrid aerogel and preparation method and application thereof in waste gas processing

Abstract

Visible-light response hybrid aerogel and a preparation method and application thereof in waste gas processing are disclosed. Dicyandiamide is taken as a precursor and is calcined in two times to prepare a carbon nitride nanosheet; the carbon nitride nanosheet is dispersed in water, silver metavanadate quantum dots are subjected to in-situ growth to prepare a silver metavanadate quantum dot/carbon nitride nanosheet composite material; the silver metavanadate quantum dot/carbon nitride nanosheet composite material and graphene oxide carry out hydrothermal reaction, and are then frozen and dried to prepare silver metavanadate quantum dot/carbon nitride nanosheet/graphene hybrid aerogel which is the visible-light response hybrid aerogel. The problems of large reduction dosage, serious secondary pollution, complexity in operation and the like generated when waste gas is processed by a traditional flue gas denitration technology are overcome.

Claims

1. A preparation method of a visible-light response hybrid aerogel, comprising the following steps: (1) using dicyandiamide as a precursor, after a first calcination and a second calcination, preparing carbon nitride nanosheets; (2) dispersing carbon nitride nanosheets in water and growing silver metavanadate quantum dots in situ to prepare silver metavanadate quantum dot/carbon nitride nanosheet composites; (3) carrying out hydrothermal reaction of silver metavanadate quantum dot/carbon nitride nanosheet composite with graphene oxide, followed by freeze-drying to prepare silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel, which is a visible-light response hybrid aerogel, wherein in the step (1), the first calcination is carried out in argon gas, a first heating rate is 5° C./min during the first calcination, and a first calcination time is 4 h, a first calcination temperature is 550° C.; and the second calcination is carried out in air, a second calcination rate is 5° C./min, a second calcination time is 2 h, and a second calcination temperature is 550° C.

2. A preparation method of silver metavanadate quantum dot/carbon nitride nanosheet composites, comprising the following steps: (1) using dicyandiamide as a precursor, after a first calcination and a second calcination, preparing carbon nitride nanosheets; (2) dispersing carbon nitride nanosheets in water and growing silver metavanadate quantum dots in situ to prepare silver metavanadate quantum dot/carbon nitride nanosheet composites, wherein in the step (1), the first calcination is carried out in argon gas, a first heating rate is 5° C./min during the first calcination, and a first calcination time is 4 h, a first calcination temperature is 550° C.; and the second calcination is carried out in air, a second calcination rate is 5° C./min, a second calcination time is 2 h, and a second calcination temperature is 550° C.

3. A method for exhaust gas treatment, comprising the following steps: (1) using dicyandiamide as a precursor, after a first calcination and a second calcination, preparing carbon nitride nanosheets; (2) dispersing carbon nitride nanosheets in water and growing silver metavanadate quantum dots in situ to prepare silver metavanadate quantum dot/carbon nitride nanosheet composites; (3) carrying out hydrothermal reaction of silver metavanadate quantum dot/carbon nitride nanosheet composite with graphene oxide, followed by freeze-drying to prepare silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel, which is a visible-light response hybrid aerogel; (4) passing the exhaust gas through the visible-light response hybrid aerogel, illuminating to complete the treatment of the exhaust gas, wherein in the step (1), the first calcination is carried out in argon gas, a first heating rate is 5° C./min during the first calcination, and a first calcination time is 4 h, a first calcination temperature is 550° C.; and the second calcination is carried out in air, a second calcination rate is 5° C./min, a second calcination time is 2 h, and a second calcination temperature is 550° C.

4. The method according to claim 1, wherein in the step (2), dispersing the carbon nitride nanosheets in water, adding silver nitrate and ammonium metavanadate, and growing silver metavanadate quantum dots in situ; the mass ratio of carbon nitride, silver nitrate and ammonium metavanadate is (18-22):(1˜2):(0.5 to 1); in situ growth is carried out in the dark, the time of in situ growth is 8˜12 h, the temperature of in situ growth is room temperature.

5. The method according to claim 4, wherein after dispersing the carbon nitride nanosheets in deionized water, adding silver nitrate and stirring for 30 min, then adding ammonium metavanadate to grow silver metavanadate quantum dots in situ, the mass ratio of carbon nitride, silver nitrate and ammonium metavanadate is 20:2:1.

6. The method according to claim 1, wherein in step (3), the mass ratio of the silver metavanadate quantum dot/carbon nitride nanosheet composite to graphene oxide is (4 to 5):(1 to 2); the temperature of the hydrothermal reaction is 95° C., the reaction time is 6 h; the temperature of freeze drying is −50° C., and the time of freeze drying is 24 h.

7. The method according to claim 6, wherein the mass ratio of the silver metavanadate quantum dot/carbon nitride nanosheet composite to graphene oxide is 3:1.

8. The visible-light response hybrid aerogel prepared by the preparation method of a visible-light response hybrid aerogel according to claim 1.

9. The application of the visible-light response hybrid aerogel according to claim 8 in the photocatalytic treatment of exhaust gas.

10. The method according to claim 2, wherein in the step (2), dispersing the carbon nitride nanosheets in water, adding silver nitrate and ammonium metavanadate, and growing silver metavanadate quantum dots in situ; the mass ratio of carbon nitride, silver nitrate and ammonium metavanadate is (18-22):(1˜2):(0.5 to 1); in situ growth is carried out in the dark, the time of in situ growth is 8˜12 h, the temperature of in situ growth is room temperature.

11. The method according to claim 3, wherein in the step (2), dispersing the carbon nitride nanosheets in water, adding silver nitrate and ammonium metavanadate, and growing silver metavanadate quantum dots in situ; the mass ratio of carbon nitride, silver nitrate and ammonium metavanadate is (18-22):(1˜2):(0.5 to 1); in situ growth is carried out in the dark, the time of in situ growth is 8˜12 h, the temperature of in situ growth is room temperature.

12. The method according to claim 10, wherein after dispersing the carbon nitride nanosheets in deionized water, adding silver nitrate and stirring for 30 min, then adding ammonium metavanadate to grow silver metavanadate quantum dots in situ, the mass ratio of carbon nitride, silver nitrate and ammonium metavanadate is 20:2:1.

13. The method according to claim 11, wherein after dispersing the carbon nitride nanosheets in deionized water, adding silver nitrate and stirring for 30 min, then adding ammonium metavanadate to grow silver metavanadate quantum dots in situ, the mass ratio of carbon nitride, silver nitrate and ammonium metavanadate is 20:2:1.

14. The method according to claim 3, wherein in step (3), the mass ratio of the silver metavanadate quantum dot/carbon nitride nanosheet composite to graphene oxide is (4 to 5):(1 to 2); the temperature of the hydrothermal reaction is 95° C., the reaction time is 6 h; the temperature of freeze drying is −50° C., and the time of freeze drying is 24 h.

15. The method according to claim 14, wherein the mass ratio of the silver metavanadate quantum dot/carbon nitride nanosheet composite to graphene oxide is 3.1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a Transmission electron microscopy image of the carbon nitride nanosheet;

(2) FIG. 2 is a Transmission electron microscopy image of silver metavanadate quantum dots/carbon nitride nanosheets;

(3) FIG. 3 is a Transmission electron microscopy image of silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel;

(4) FIG. 4 is a Scanning electron microscopy image of the silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel;

(5) FIG. 5 is a catalytic effect diagram of silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel with different loading qualities;

(6) FIG. 6 is a catalytic effect diagram of silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel with different loading qualities;

(7) FIG. 7 is a catalytic cycle diagram of silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

(8) The preparation of carbon nitride nanosheets, the steps are as follows:

(9) 10 g of dicyandiamide is placed in a tube furnace and calcined under Ar gas atmosphere, and then heated to 550° C. for 4 h at a heating rate of 5° C./min to obtain the bulk carbon nitride; the bulk carbon nitride is calcined in air, and heated to 550° C. for 2 h at a heating rate of 5° C./min. The present invention uses calcination to obtain carbon nitride nanosheets with a large specific surface area. FIG. 1 is a Transmission electron microscopy image of the carbon nitride nanosheet.

Embodiment 2

(10) The preparation of silver metavanadate quantum dots/carbon nitride nanosheets is as follows:

(11) Silver nitrate (0.0170 g, 0.1 mmol) is dissolved in 20 ml of deionized water using a foil-wrapped beaker, and then carbon nitride nanosheets (0.1 g) is added to the solution and stirred for 30 minutes, the obtained suspension is then sonicated for 1 hour. 20 ml of ammonium metavanadate aqueous solution (0.0117 g, 0.1 mmol) is added to the suspension by a disposable syringe (20 ml) at a rate of 60 ml/h, and then the pH is adjusted to neutral and sonicated for 1 hour, and stirred in an oil bath for 8 hours. Finally, it is washed three times with deionized water and absolute ethanol. The product is placed in an oven at 80° C. for 8 h to prepare silver metavanadate quantum dots/carbon nitride nanosheets, which is recorded as AVO-CN. According to the quality of the added carbon nitride nanosheets, the composite materials with different loading quality of silver vanadate can be obtained, such as AVO.sub.10-CN (loading mass of silver vanadate is 10 wt %), AVO.sub.20-CN, AVO.sub.30-CN, AVO.sub.40-CN; FIG. 2 shows the Transmission electron microscopy image of silver metavanadate quantum dots/carbon nitride nanosheets.

Embodiment 3

(12) Preparation of silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel is as follows:

(13) 15 mg of graphene oxide is added to a glass bottle (20 ml) and 4 ml of water is added thereto to uniformly disperse, then 45 mg of AVO.sub.30-CN is added to the graphene oxide dispersion. After ultrasonic mixing, 30 mg of L-ascorbic acid is added, and the mixture is placed in boiling water for half an hour to form a hydrogel and immediately frozen in a −40° C. refrigerator for 40 min. After natural melting, it is placed in a boiling water bath for 8 hours, and finally freeze-dried in a freeze dryer for two days to obtain a regular shape of light aerogel hybrid silver metavanadate quantum dots/carbon nitride nanosheets/graphene, which is denoted as AVO.sub.30-CN-GA-75 (AVO.sub.30-CN mass fraction is 75 wt %). According to the quality of the addition of graphene oxide, aerogel with different AVO.sub.30-CN mass loading can be prepared, denoted as AVO.sub.30-CN-GA-50, AVO.sub.30-CN-GA-75, AVO.sub.30-CN-GA-90. FIG. 3 shows the Transmission electron microscopy image of silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel; FIG. 4 is a Scanning electron microscopy image of the silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel.

Embodiment 4

(14) Photocatalytic degradation, the specific steps are as follows:

(15) Place 50 mg of catalyst in the center of a closed cylindrical reactor with a volume of 1.6 L. The xenon lamp is placed vertically above the reactor. The nitric oxide gas is supplied from a concentrated gas cylinder, and the air flow supplied through the compressed air cylinder is diluted to 600 ppb. The two gas streams are premixed in a three-way valve with a flow rate controlled at 2.4 L/min. When the catalyst, gas and water vapor reach the adsorption-desorption equilibrium within half an hour, turn on the 300 w xenon lamp, use the NOx analyzer, the measurement time is 30 min, the concentration interval detected by the instrument is 1 min, and finally calculate the removal efficiency based on the measured concentration data. FIG. 5 and FIG. 6 show catalytic diagrams of silver metavanadate quantum dots/carbon nitride nanosheets/graphene hybrid aerogel with different loading qualities; FIG. 7 is a catalytic cycle diagram of silver metavanadate quantum dot/carbon nitride nanosheet/graphene hybrid aerogel.

(16) The photocatalytic oxidation method of the invention has mild reaction conditions, low energy consumption, and the oxidation route is consistent with the nitrogen fixation process having a positive effect in the natural world, and thus can be widely used in the field of pollutant degradation; among them, carbon nitride is used for photocatalytic treatment of exhaust gas. It has high visible light absorption and degradation efficiency, and its modification can inhibit the recombination of electron-hole pairs and improve the catalytic efficiency.