Modified g-C3N4 heterojunction photocatalytic self-cleaning coating as well as preparation method and application thereof

Abstract

The invention discloses a modified g-C3N4 heterojunction photocatalytic self-cleaning coating and a preparation method and application thereof.According to the coating, graphite phase carbon nitride g-C3N4 and bismuth titanate form an S-type heterojunction, the coating is of a lamellar structure, and the outermost layer is coated with polydimethylsiloxane; the preparation method comprises the following steps: (1) carrying out hydrothermal reaction on bismuth titanate and graphite phase carbon nitride to obtain a graphite phase carbon nitride nanosheet / bismuth titanate nanosheet S-type heterojunction photocatalyst; and (2) coating the surface of the catalyst with a polydimethylsiloxane prepolymer to obtain a product. The graphite-phase carbon nitride nanosheet is combined with bismuth titanate, and an S-shaped heterojunction is constructed, so that the utilization efficiency of solar visible light is remarkably improved, an oxidation-reduction reaction can be efficiently catalyzed under the irradiation of visible light, organic pollutants on the surface of the coating can be decomposed, and the coating has a self-cleaning capability by coating polydimethylsiloxane; and the removal cost of the organic pollutants is reduced.

Description

Technical Field

[0001] The present invention relates to a coating material, and particularly to a modified g-C3N4 heterojunction photocatalytic self-cleaning coating and its preparation method and application. Background Art

[0002] The self-cleaning performance depends on the wettability of the coating surface, including superhydrophobic effect and superhydrophilic effect. The superhydrophilic surface is easily contaminated by ash when painted on the exterior wall surface, which is not conducive to the degradation of photocatalytic reactions. The superhydrophobic coating is composed of micro-nano structures and layered materials with low surface energy, and has excellent water repellency and anti-fouling performance. In practical applications, it can achieve self-cleaning effects by the free rolling of water to adsorb pollutants such as dust on the material surface, and is more suitable for exterior wall self-cleaning coatings. Therefore, it is of great significance to develop a coating that combines photocatalysis and self-cleaning.

[0003] Among various catalytic materials, graphitic carbon nitride is a metal-free photocatalyst with appropriate energy band edges and a large energy band gap, which can respond within the visible light wavelength range and can catalyze various reactions, such as photocatalytic degradation of organic pollutants or photochemical decomposition of water. However, graphitic carbon nitride directly synthesized by polycondensation reaction usually has a very low surface area and poor photocatalytic activity. The main reason is that the graphitic carbon nitride prepared by polycondensation reaction has serious agglomeration effects, resulting in easy agglomeration of photogenerated electrons and holes, which greatly affects the photocatalytic effect of the material. Therefore, the application of graphitic carbon nitride alone in the field of photocatalysis is very limited. Summary of the Invention

[0004] Object of the Invention: The first object of the present invention is to provide a modified g-C3N4 heterojunction photocatalytic self-cleaning coating that improves the catalytic activity of g-C3N4 and has a self-cleaning function; the second object of the present invention is to provide a preparation method for the modified g-C3N4 heterojunction photocatalytic self-cleaning coating; the third object of the present invention is to provide the application of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating.

[0005] Technical Solution: The modified g-C3N4 heterojunction photocatalytic self-cleaning coating of the present invention consists of graphitic carbon nitride g-C3N4 and bismuth titanate (Bi4Ti3O 10 ) to form an S-type heterojunction, presenting a lamellar structure, and the outermost layer is coated with polydimethylsiloxane.

[0006] Preferably, the mass of the graphitic carbon nitride g-C3N4 is 5-15% of the mass of bismuth titanate. With the increase of the content of graphene carbon nitride, the catalytic degradation efficiency of organic matter first increases and then decreases, and the catalytic degradation efficiency is the highest when the content of graphitic carbon nitride is 10wt%.

[0007] Preferably, the graphitic carbon nitride has a porous structure.

[0008] The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating described in the present invention includes the following steps:

[0009] (1) Dissolve bismuth titanate in an aqueous solution, add a graphite-phase carbon nitride suspension, and perform a hydrothermal reaction on the mixed suspension to obtain a graphite-phase carbon nitride nanosheet / bismuth titanate nanosheet S-type heterojunction photocatalyst;

[0010] (2) Mix the graphite-phase carbon nitride nanosheet / bismuth titanate nanosheet S-type heterojunction photocatalyst, polydimethylsiloxane prepolymer, and ammonium bicarbonate evenly, and perform a polymerization reaction to obtain the modified g-C3N4 heterojunction photocatalytic self-cleaning coating.

[0011] Preferably, in step (1), the temperature of the hydrothermal reaction is 180-220 °C, and the reaction time is 5-7 h.

[0012] Preferably, after the hydrothermal reaction in step (1) is completed, the obtained sample is alternately centrifuged and washed with water and ethanol 5 times to remove the salts therein, and then dried in an oven.

[0013] Preferably, the temperature of the polymerization reaction is 70-90 °C, and the reaction time is 1-2.5 h.

[0014] Preferably, the graphite-phase carbon nitride suspension is: adding graphite-phase carbon nitride to ethanol to form a suspension.

[0015] Preferably, the preparation method of the graphite-phase carbon nitride is: placing melamine in a quartz crucible, placing it under a tubular furnace and passing a N2 flow, and calcining at 500-600 °C for 3-5 h.

[0016] Preferably, the preparation method of the bismuth titanate nanosheets is: mixing bismuth oxide, titanium dioxide, potassium chloride, and sodium chloride, grinding them, and then placing them in a tubular furnace and calcining at 750-850 °C for 1.5-2.5 h; the heating rate of the tubular furnace is 10 °C / min.

[0017] The application of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating described in the present invention in the self-cleaning of degrading organic pollutants.

[0018] Preferably, the organic pollutant is Rhodamine B.

[0019] Invention mechanism:

[0020] To improve the photocatalytic performance of g-C3N4, a composite material design method is adopted to combine it with bismuth titanate. Bismuth titanate is a typical Aurivllius bismuth layered structure compound, a semiconductor material with a relatively wide bandgap (about 3.2 eV), having good optical and electrical properties, especially with strong light absorption ability in the ultraviolet and visible light regions. Therefore, the combination of g-C3N4 and bismuth titanate can give full play to the advantages of both and improve the photocatalytic efficiency.

[0021] The S-type heterojunction structure further optimizes the electron transport between materials and the separation efficiency of photo-generated carriers. Through bandgap differences and energy band alignment, the S-type heterojunction can effectively promote the separation of electrons and holes under light illumination, reduce the recombination effect, and enhance the photocatalytic performance. After the combination of g-C3N4 and bismuth titanate, the formation of the S-type heterojunction can effectively improve the photocatalytic performance of the composite material, especially in aspects such as water splitting, air purification, and environmental remediation.

[0022] The photocatalytic self-cleaning coating prepared by the method of the present invention successfully constructs a graphite-phase carbon nitride nanosheet / bismuth titanate nanosheet S-type heterojunction structure and realizes the construction of a superhydrophobic surface by a one-step green preparation method. This coating can effectively protect the substrate material, while showing excellent catalytic performance and strong substrate adhesion, and has excellent durability. The porous structure of the graphite-phase carbon nitride / bismuth titanate S-type heterojunction significantly improves the utilization efficiency of solar visible light, can efficiently catalyze redox reactions under visible light irradiation, decompose organic pollutants on the coating surface, and constructs a low surface energy coating by a deposition method, with a simple process, being green and environmentally friendly, and no polluting intermediate products are generated. This method has no special requirements for the shape and size of the substrate, is applicable to various types of substrates, and has a wide application prospect. Combining the superhydrophobic surface characteristics, the present invention realizes the self-cleaning effect and significantly reduces the cost of removing organic pollutants.

[0023] Advantages: Compared with the prior art, the present invention has the following remarkable advantages: (1) By combining graphite-phase carbon nitride nanosheets with bismuth titanate and constructing an S-type heterojunction, the utilization efficiency of solar visible light is significantly improved, redox reactions can be efficiently catalyzed under visible light irradiation to decompose organic pollutants on the coating surface, and coating with polydimethylsiloxane endows the coating with self-cleaning ability, reducing the cost of removing organic pollutants; (2) Constructing a low surface energy coating by a deposition method, with a simple process, being green and environmentally friendly, and no polluting intermediate products are generated; (3) The coating has no special requirements for the shape and size of the substrate, is applicable to various types of substrates, and has a wide application prospect. Description of the Drawings

[0024] Figure 1It is the scanning electron microscope image of the 10 wt% g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in step (3) of Example 2 of the present invention;

[0025] Figure 2 It is the EDS elemental analysis image of the 10 wt% g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in step (3) of Example 2 of the present invention;

[0026] Figure 3 It is the band gap diagram of the 10 wt% g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in step (3) of Example 2 of the present invention;

[0027] Figure 4 It is the photocatalytic activity curve diagram of the g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in step (3) of Examples 1-3 of the present invention, g-C3N4 prepared in Comparative Example 1, and BTO prepared in Comparative Example 2 for degrading a 50 ml rhodamine B solution with a concentration of 12 mg / L after 30 min of dark reaction under visible light irradiation;

[0028] Figure 5 It is the water contact angle diagram of the g-C3N4 / BTO composite S-scheme heterojunction photocatalytic self-cleaning coating prepared in step (5) of Example 2 of the present invention;

[0029] Figure 6 It is the water contact angle diagram of the g-C3N4 / BTO composite S-scheme heterojunction photocatalytic self-cleaning coating prepared in step (5) of Example 2 of the present invention after 20 wear-resistant cycles for 90 d; Detailed implementation manners

[0030] The technical solutions of the present invention will be further described below in conjunction with the embodiments.

[0031] Example 1

[0032] The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating of the present invention includes the following steps:

[0033] (1) Place 20 g of dry melamine powder in a quartz crucible, calcine it in a tube furnace at a heating rate of 5 °C / min for 4 h to 550 °C, and keep the roasting for 2 h to obtain graphitic carbon nitride;

[0034] (2) Weigh Bi2O3, TiO2, NaCl, and KCl according to a molar ratio of 2:3:150:150, grind for 30 min, then calcine at 800 °C for 120 min (10 °C / min), wash the obtained sample 5 times by centrifugation with water and ethanol alternately to remove the salts therein, and then dry it in an oven to obtain bismuth titanate (BTO) powder;

[0035] (3) Dissolve 0.5 g of the prepared BTO powder in 20 mL of water, then slowly add it to 20 mL of an ethanol solution containing 0.025 g of g-C3N4, sonicate for 1 h, seal the mixed suspension in a polytetrafluoroethylene autoclave, carry out a hydrothermal reaction at 200 °C for 6 h, and dry at 50 °C to obtain a graphite-phase carbon nitride nanosheet / bismuth titanate nanosheet S-scheme heterojunction photocatalyst;

[0036] (4) Mix 22 g of ammonium bicarbonate, 11 g of polydimethylsiloxane prepolymer (the ratio of PDMS base to curing agent is 10:1 w / w) with the graphite-phase carbon nitride nanosheet / bismuth titanate nanosheet S-scheme heterojunction photocatalyst prepared in step (3) and stir evenly to obtain a coating material.

[0037] (5) Apply the coating material to the mortar

[0038] Then coat the coating material on the mortar (the coating thickness is 5 mm), place it in a sealed container at a temperature of 80 °C for 90 min; wash the coated mortar under ultrasonic waves for 10 min, and finally dry it in an oven at 80 °C for 60 min to obtain the modified g-C3N4 heterojunction photocatalytic self-cleaning coating, denoted as 5 wt% g-C3N4 / BTO.

[0039] Example 2

[0040] The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating of the present invention includes the following steps:

[0041] (1) Place 20 g of dry melamine powder in a quartz crucible, calcine it in a tubular furnace at a heating rate of 5 °C / min for 4 h to 550 °C, and keep roasting for 2 h to obtain graphite-phase carbon nitride;

[0042] (2) Weigh Bi2O3, TiO2, NaCl and KCl according to a molar ratio of 2﹕3﹕150﹕150, grind for 30 min, then calcine at 800 °C for 120 min (10 °C / min), wash the obtained sample 5 times by centrifugation with water and ethanol alternately to remove the salts therein, and then dry it in an oven to obtain bismuth titanate (BTO) powder;

[0043] (3) Dissolve 0.5 g of the prepared BTO powder in 20 ml of water, then slowly add it to 20 ml of an ethanol solution containing 0.05 g of g-C3N4, sonicate for 1 h, seal the mixed suspension in a polytetrafluoroethylene autoclave, carry out a hydrothermal reaction at 200 °C for 6 h, and dry at 50 °C to obtain a graphite-phase carbon nitride nanosheet / bismuth titanate nanosheet S-scheme heterojunction photocatalyst;

[0044] (4) Mix 22 g of ammonium bicarbonate and 11 g of polydimethylsiloxane prepolymer (the ratio of base to curing agent in PDMS is 10:1 w / w), and stir well with the graphite carbon nitride nanosheet / bismuth titanate nanosheet S-type heterojunction photocatalyst prepared in step (3) to obtain a coating material.

[0045] (5) Apply the coating material to the mortar

[0046] Then apply the coating material to the mortar (the coating thickness is 5 mm), place it in a sealed container at a temperature of 80 °C for 90 min; wash the coated mortar under ultrasonic waves for 10 min, and then dry it in an oven at 80 °C for 60 min, denoted as 10 wt% g-C3N4 / BTO.

[0047] Example 3

[0048] The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating of the present invention includes the following steps:

[0049] (1) Place the powder obtained by drying 20 g of melamine in a quartz crucible, calcine it in a tube furnace at a heating rate of 5 °C / min for 4 h to 550 °C, and keep roasting for 2 h to obtain graphite carbon nitride;

[0050] (2) Weigh Bi2O3, TiO2, NaCl and KCl according to a molar ratio of 2﹕3﹕150﹕150, grind for 30 min, and then calcine at 800 °C for 120 min (10 °C / min). Wash the obtained sample 5 times by alternating centrifugation with water and ethanol to remove the salts therein, and then dry it in an oven to obtain bismuth titanate (BTO) powder;

[0051] (3) Dissolve 0.5 g of the prepared BTO powder in 20 ml of water, then slowly add it to a 20 ml ethanol suspension containing 0.075 g of g-C3N4, sonicate for 1 h, seal the mixed suspension in a polytetrafluoroethylene autoclave, carry out a hydrothermal reaction at 200 °C for 6 h, and dry it at 50 °C to obtain a graphite carbon nitride nanosheet / bismuth titanate nanosheet S-type heterojunction photocatalyst;

[0052] (4) Mix 22 g of ammonium bicarbonate and 11 g of polydimethylsiloxane prepolymer (the ratio of base to curing agent in PDMS is 10:1 w / w), and stir well with the graphite carbon nitride nanosheet / bismuth titanate nanosheet S-type heterojunction photocatalyst prepared in step (3) to obtain a coating material.

[0053] (5) Apply the coating material to the mortar

[0054] Then, the coating material was coated on the mortar (the coating thickness was 5 mm), placed in a sealed container at a temperature of 80 °C for 90 min. The coated mortar was washed under ultrasonic waves for 10 min and then dried in an oven at 80 °C for 60 min, denoted as 15 wt% g-C3N4 / BTO.

[0055] Comparative Example 1

[0056] Based on Example 1, only step (1) was carried out to obtain graphitic carbon nitride g-C3N4.

[0057] Comparative Example 2

[0058] Based on Example 1, only step (2) was carried out to obtain bismuth titanate (BTO) powder.

[0059] Structural Characterization

[0060] The g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in step (3) of Example 2 was characterized, and the results are as Figure 1 and Figure 2 shown.

[0061] Figure 1 is the scanning electron microscope image of the g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in Example 2. It can be seen from the figure that the prepared g-C3N4 / BTO composite S-scheme photocatalytic heterojunction is a lamellar superposition structure.

[0062] Figure 2 is the EDS elemental analysis diagram of the g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in Example 2. The C and N elements in the figure indicate that the heterojunction contains g-C3N4, and the Bi, Ti, and O elements in the figure indicate that the heterojunction contains bismuth titanate, indicating that the prepared S-scheme heterojunction is composed of the composite of g-C3N4 and bismuth titanate.

[0063] Performance Characterization

[0064] 1. Spectral Property Test

[0065] Figure 3 is the band gap diagram of the 10 wt% g-C3N4 / BTO composite S-scheme heterojunction photocatalyst prepared in Example 2. It can be seen from the figure that its band gap is about 3.67 eV. Compared with the band gap of pure graphitic carbon nitride of about 2.7 eV and the band gap of pure bismuth titanate of about 3.2 eV, it conforms to the characteristics of the S-scheme heterojunction, broadening the band gap while maintaining excellent redox ability.

[0066] 2. Performance Test of Catalyst for Degrading Organic Compounds

[0067] Test method: 0.1 g of 5 wt% g-C3N4 / BTO composite S-scheme heterojunction photocatalyst (Example 1), 10 wt% g-C3N4 / BTO composite S-scheme heterojunction photocatalyst (Example 2), 15 wt% g-C3N4 / BTO composite S-scheme heterojunction photocatalyst (Example 3), g-C3N4 prepared in Comparative Example 1, and BTO prepared in Comparative Example 2 were added to a rhodamine B solution of 12 mg / L respectively. Irradiation was carried out with a 300 W xenon lamp. A sample was taken after 30 min of dark reaction, and then samples were taken every 30 min during the photocatalytic reaction to test the concentration of the rhodamine B solution. The test results are as Figure 4 shown.

[0068] It can be Figure 4 seen that under visible light irradiation, the degradation efficiencies of 5 wt% g-C3N4 / BTO (Example 1), 10 wt% g-C3N4 / BTO (Example 2), 15 wt% g-C3N4 / BTO (Example 3), g-C3N4 (Comparative Example 1), and BTO (Comparative Example 2) for rhodamine B were 32.9%, 47.7%, 31.3%, 25.8%, and 35.2% respectively at 30 min; and the degradation efficiencies were 94.67%, 97.5%, 97.3%, 91.2%, and 92% respectively at 180 min. The 10 wt% g-C3N4 / BTO in Example 2 had the best photocatalytic degradation efficiency, and the degradation efficiency was the best at each time point. The g-C3N4 / BTO composite S-scheme heterojunction photocatalysts prepared in Examples 1 to 3 almost completely degraded the 12 mg / L rhodamine B solution. In the early stage, BTO in Comparative Example 2 adsorbed more rhodamine B, so the degradation efficiency was slightly higher than that of Examples 1 and 2 in the early stage, but the complete degradation efficiency was lower than that of Examples 1 and 2. It can be seen that the g-C3N4 / BTO composite S-scheme photocatalysts in Examples 1 to 3 had a higher degradation efficiency for rhodamine B than the single photocatalysts of g-C3N4 in Comparative Example 1 and BTO in Comparative Example 2.

[0069] 3. Surface hydrophobicity test

[0070] It can be Figure 5 seen that the hydrophobic angle of the g-C3N4 / BTO composite S-scheme photocatalytic self-cleaning coating prepared in step (5) of Example 2 was 157°, showing self-cleaning superhydrophobicity.

[0071] It can be Figure 6 seen that the hydrophobic angle of the g-C3N4 / BTO composite S-scheme photocatalytic self-cleaning coating prepared in step (5) of Example 2 was still 141.7° after 20 wear-resistant cycles and 90 d of durability treatment, showing excellent wear resistance and durability.

Claims

1. A modified g-C3N4 heterojunction photocatalytic self-cleaning coating, characterized in that, An S-scheme heterojunction composed of graphitic carbon nitride g-C3N4 and bismuth titanate presents a lamellar structure, and the outermost layer is coated with polydimethylsiloxane.

2. The modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to claim 1, wherein The mass of the graphitic carbon nitride g-C3N4 is 5-15% of the mass of bismuth titanate.

3. The modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to claim 1, characterized in that, The graphitic carbon nitride has a porous structure.

4. A method for preparing the modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to any one of claims 1 to 3, characterized in that, It includes the following steps: (1) Dissolve bismuth titanate in an aqueous solution, add a suspension of graphitic carbon nitride, and perform a hydrothermal reaction on the mixed suspension to obtain a graphitic carbon nitride nanosheet / bismuth titanate nanosheet S-scheme heterojunction photocatalyst; (2) Mix the graphitic carbon nitride nanosheet / bismuth titanate nanosheet S-scheme heterojunction photocatalyst, polydimethylsiloxane prepolymer, and ammonium bicarbonate evenly, and carry out a polymerization reaction to obtain the modified g-C3N4 heterojunction photocatalytic self-cleaning coating.

5. The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to claim 4, wherein, In step (1), the temperature of the hydrothermal reaction is 180-220 °C, and the reaction time is 5-7 h.

6. The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to claim 4, characterized in that, The temperature of the polymerization reaction is 70-90 °C, and the reaction time is 1-2.5 h.

7. The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to claim 4, characterized in that, In step (1), the preparation method of the graphitic carbon nitride is as follows: Place melamine in a quartz crucible, place it under a nitrogen flow in a tube furnace, and calcine it at 500-600 °C for 3-5 h.

8. The preparation method of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to claim 4, characterized in that, In step (1), the preparation method of the bismuth titanate is as follows: Mix bismuth oxide, titanium dioxide, potassium chloride, and sodium chloride, grind them, and place them in a tube furnace for calcination at 750-850 °C for 1.5-2.5 h.

9. Application of the modified g-C3N4 heterojunction photocatalytic self-cleaning coating according to any one of claims 1-3 in the self-cleaning of degrading organic pollutants.

10. The application according to claim 9, characterized in that, The organic pollutant is rhodamine B.

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