Preparation method of carbon nitride / titanium dioxide composite photocatalyst

Abstract

The application discloses a preparation method of a carbon nitride / titanium dioxide composite photocatalyst, which comprises carbon nitride preparation, titanium dioxide cleaning and catalyst compounding. The precursor is calcined to 250 DEG C and kept warm in a nitrogen atmosphere, so that carbon-nitrogen single bonds and double bonds in the precursor are in a molecular active state. Then, the precursor is heated to 550-600 DEG C, so that the precursor is rapidly decomposed to generate flaky carbon nitride. The carbon nitride is subjected to high-pressure alkali treatment, so that unstable nitrogen-hydrogen compounds on the surface of the carbon nitride are removed, thereby forming part of vacancies. The titanium dioxide is subjected to ultrasonic alkali soaking treatment, so that free-state organic matters on the surface of the titanium dioxide are removed and hydroxyl groups are introduced. Finally, a wet ball mill is used for catalyst compounding. Through the above steps, the transition time of the precursor from a stable state to a decomposition state can be effectively shortened, the specification of the carbon nitride is relatively regular and uniform, the generation of flaky carbon nitride is facilitated, and then the performance of the composite photocatalyst is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of composite photocatalyst production, in particular to a preparation method of a carbon nitride-titanium dioxide composite photocatalyst. BACKGROUND

[0002] With the rapid growth of modern industrialization and population, energy shortage and environmental problems force people to pay more and more attention to the development and utilization of clean energy, reduce the pollution to the environment, and the semiconductor photocatalytic technology is considered as one of the most possible methods to solve the energy shortage and degrade pollutants, which takes clean solar energy as the driving force of the catalytic reaction. And the preparation of semiconductor photocatalyst with low cost, excellent performance and wide visible light response range is the key, which determines whether it can be widely applied. Through element doping and dye sensitization, the effective utilization of sunlight by the semiconductor is improved, and the purpose of improving environmental pollution is achieved.

[0003] Among numerous catalysts, nano-TiO2 has been widely applied and studied due to its stable structure, non-toxicity and low price. However, due to its wide band gap (3.2 eV), it can only absorb ultraviolet light and has almost no response to visible light, resulting in low catalytic efficiency. As the most stable phase at room temperature, graphite phase carbon nitride (g-C3N4) has attracted extensive attention due to its unique electronic structure and characteristics. Its band gap is relatively narrow (2.7 eV) and has strong visible light absorption capacity. However, the small specific surface area and high recombination rate of photo-generated electrons and holes of g-C3N4 are difficult problems for improving its photocatalytic efficiency. Studies have found that the formation of a semiconductor heterojunction by combining two different catalysts with appropriate valence band (VB) and conduction band (CB) potentials can enhance the photocatalytic activity of g-C3N4-based semiconductors. However, how to improve the crystallinity of g-C3N4 and the effective combination of two semiconductors are still research hotspots in the field of photocatalysis.

[0004] In the existing production process, the production of carbon nitride takes a long time, is easy to agglomerate into blocks, and it is difficult to obtain sheet-shaped carbon nitride, so that the photocatalytic performance is difficult to achieve the expected effect. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a carbon nitride-titanium dioxide composite photocatalyst to solve the problems raised in the background art.

[0006] To achieve the above purpose, the present application provides the following technical scheme: a preparation method of a carbon nitride-titanium dioxide composite photocatalyst, comprising carbon nitride preparation and titanium dioxide cleaning.

[0007] The carbon nitride preparation comprises the following steps:

[0008] T1, decomposition preparation of the precursor: the precursor is baked from room temperature to 250 DEG C under nitrogen atmosphere, and is kept for 1-3 hours;

[0009] T2, decomposition of the precursor: the precursor kept for 1 hour is continuously baked from 250 DEG C to 550-600 DEG C under nitrogen atmosphere, and is kept for 3-6 hours, then is cooled to room temperature, and carbon nitride is obtained;

[0010] T3, high-pressure alkali treatment: the obtained carbon nitride is placed into 5-10 mol / L sodium hydroxide solution, the pressure is kept at 5-10 MPa, and the time is kept for 6-8 hours at 60 DEG C;

[0011] The titanium dioxide cleaning comprises the following steps:

[0012] T1, the titanium dioxide is subjected to alkali soaking treatment, and the time is 6-10 hours;

[0013] Further comprising catalyst compounding, comprising the following steps:

[0014] S1, the carbon nitride and the titanium dioxide are mixed in air atmosphere, and are baked for 1-6 hours at 400-500 DEG C, and are cooled to room temperature;

[0015] S2, the carbon nitride and the titanium dioxide mixture at room temperature are placed into a wet ball mill, the wet ball mill is operated at 20-40 r / min, and the operation time is 3-6 hours.

[0016] Preferably, the precursor comprises melamine or urea.

[0017] Preferably, in the decomposition preparation of the precursor, the heating rate is 3-15 DEG C / min.

[0018] Preferably, in the decomposition of the precursor, the heating rate is 5-20 DEG C / min.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] The present application discloses a preparation method of carbon nitride titanium dioxide composite photocatalyst, through the heat preservation stage of the precursor, the residual water and part of free compounds in the precursor can be removed, the carbon-nitrogen single bond and double bond in the precursor are in a molecular active state, then through baking, the transition time of the precursor from stable state to decomposition state can be effectively shortened, the carbon nitride is relatively regular and uniform, which is beneficial to the generation of flaky carbon nitride, and further beneficial to the improvement of the performance of the composite photocatalyst. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The present application discloses a preparation method of carbon nitride titanium dioxide composite photocatalyst, through the heat preservation stage of the precursor, the residual water and part of free compounds in the precursor can be removed, the carbon-nitrogen single bond and double bond in the precursor are in a molecular active state, then through baking, the transition time of the precursor from stable state to decomposition state can be effectively shortened, the carbon nitride is relatively regular and uniform, which is beneficial to the generation of flaky carbon nitride, and further beneficial to the improvement of the performance of the composite photocatalyst. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0023] Please refer to Figure 1 The present embodiment provides a preparation method of a carbon nitride / titanium dioxide composite photocatalyst, which comprises carbon nitride preparation, titanium dioxide cleaning and catalyst compounding.

[0024] The carbon nitride preparation comprises the following steps:

[0025] T1, decomposition preparation of the precursor: in a nitrogen atmosphere, the precursor is calcined from room temperature to 250°C at a heating rate of 3-15°C / min, and is kept for 1 hour. The precursor can be melamine or urea.

[0026] Taking melamine as the precursor, through the heat preservation stage of the precursor, the residual moisture and part of the free compounds in the melamine can be removed, so as to prepare for the decomposition of the melamine, make the carbon-nitrogen single bond and double bond in the melamine in a molecular active state, and not easy to produce toxic cyanide in the subsequent thermal cracking.

[0027] T2, decomposition of the precursor: in a nitrogen atmosphere, the precursor after being kept for 1 hour is continuously calcined at a heating rate of 5-20°C / min, from 250°C to 550-600°C, so that the melamine is rapidly decomposed to generate flaky carbon nitride, and is kept for 3-6 hours and then cooled to room temperature. Since the transition time from the stable state to the decomposition state is short, the specification of the carbon nitride is relatively regular and uniform.

[0028] T3, high-pressure alkali treatment: the obtained carbon nitride is placed in a 5-10 mol / L sodium hydroxide solution, the pressure is kept at 5-10 MPa, and the duration is 6-8 hours at a temperature of 60°C. The high pressure can control the band gap width of the carbon nitride, significantly enhance the photocatalytic activity, and at the same time, through the alkali treatment, the unstable nitrogen-hydrogen compounds on the surface of the carbon nitride can be removed, so as to form part of vacancies, and facilitate the formation of a heterojunction structure.

[0029] The carbon nitride treated by the high-pressure alkali treatment can be indicated by the hydrogen production index to indicate the heterojunction structure.

[0030] The titanium dioxide cleaning comprises the following steps:

[0031] T1, titanium dioxide is subjected to alkali soaking treatment for 6-10 hours to remove free-state organic matter on the surface of the titanium dioxide and introduce hydroxyl groups;

[0032] Catalyst compounding, comprising the following steps:

[0033] S1, carbon nitride and titanium dioxide are mixed in an air atmosphere and calcined at 400-500°C for 1-6 hours and cooled to room temperature;

[0034] S2, the room temperature carbon nitride and titanium dioxide mixture is placed in a wet ball mill in an air atmosphere, the wet ball mill is operated at 20-40 r / min for 3-6 hours.

[0035] S3, the milled slurry is spray dried to obtain the final sample.

[0036] Example 1

[0037] T1, decomposition preparation of the precursor: melamine is calcined from room temperature to 250°C at a heating rate of 12°C / min in a nitrogen atmosphere and held for 1 hour.

[0038] T2, decomposition of the precursor: the melamine held for 1 hour is further calcined from 250°C to 580°C at a heating rate of 10°C / min in a nitrogen atmosphere and held for 4 hours to rapidly decompose the melamine into flaky carbon nitride.

[0039] T3, the obtained carbon nitride is placed in a 6 mol / L sodium hydroxide solution, the pressure is maintained at 8 MPa, and the duration is 7 hours at a temperature of 60°C.

[0040] T4, titanium dioxide is subjected to ultrasonic alkali soaking treatment for 8 hours to remove free-state organic matter on the surface of the titanium dioxide and introduce hydroxyl groups.

[0041] T5, the room temperature carbon nitride and titanium dioxide mixture is placed in a wet ball mill in an air atmosphere, the wet ball mill is operated at 36 r / min for 5 hours.

[0042] T6, the milled slurry is spray dried to obtain the final sample.

[0043] Example 2

[0044] T1, decomposition preparation of the precursor: urea is calcined from room temperature to 250°C at a heating rate of 8°C / min in a nitrogen atmosphere and held for 1.6 hours.

[0045] T2, Decomposition of the precursor: The urea after 1.6 hours of heat preservation was continuously calcined at a temperature increasing rate of 16℃ / min from 250℃ to 550℃ under nitrogen atmosphere, so that the urea was rapidly decomposed to generate flaky carbon nitride.

[0046] T3, The obtained carbon nitride was placed into a 10 mol / L sodium hydroxide solution under the condition of a temperature of 60℃ for 8 hours.

[0047] T4, The titanium dioxide was subjected to ultrasonic alkali soaking treatment, the pressure was kept at 6MPa, and the time was 7 hours, so that the free state organic matter on the surface of the titanium dioxide was removed and hydroxyl groups were introduced.

[0048] The mixture of the carbon nitride and the titanium dioxide at room temperature was placed into a wet ball mill under air atmosphere, the wet ball mill was operated at 33r / min for 4 hours.

[0049] T5, The slurry after ball milling was subjected to spray drying, so that the final sample was obtained.

[0050] Example 3

[0051] T1, Decomposition preparation of the precursor: The melamine was calcined from room temperature to 250℃ at a temperature increasing rate of 15℃ / min under nitrogen atmosphere, and was heat preserved for 3 hours.

[0052] T2, Decomposition of the precursor: The melamine after 3 hours of heat preservation was continuously calcined at a temperature increasing rate of 20℃ / min from 250℃ to 600℃ under nitrogen atmosphere, so that the melamine was rapidly decomposed to generate flaky carbon nitride.

[0053] T3, The obtained carbon nitride was placed into a 7 mol / L sodium hydroxide solution, the pressure was kept at 8MPa, and the time was 6.5 hours under the condition of a temperature of 60℃.

[0054] T4, The titanium dioxide was subjected to ultrasonic alkali soaking treatment, and the time was 6 hours, so that the free state organic matter on the surface of the titanium dioxide was removed and hydroxyl groups were introduced.

[0055] T5, The mixture of the carbon nitride and the titanium dioxide at room temperature was placed into a wet ball mill under air atmosphere, the wet ball mill was operated at 30r / min for 6 hours.

[0056] T6, The slurry after ball milling was subjected to spray drying, so that the final sample was obtained.

[0057] Comparative Example 1

[0058] T1, Decomposition preparation of the precursor: The melamine was calcined from room temperature to 550℃ at a temperature increasing rate of 3℃ / min under nitrogen atmosphere, and was heat preserved for 3 hours, and the carbon nitride precursor was obtained after cooling.

[0059] T2, the obtained carbon nitride is placed into a 7 mol / L sodium hydroxide solution, the pressure is kept at 8 MPa, and the temperature is kept at 60°C for 6.5 hours.

[0060] T3, the titanium dioxide is subjected to ultrasonic alkali soaking treatment for 6 hours to remove free-state organic matter on the surface of the titanium dioxide and introduce hydroxyl groups.

[0061] T4, the mixture of the carbon nitride and the titanium dioxide at room temperature is placed into a wet ball mill in an air atmosphere, the wet ball mill is operated at 20 r / min for 8 hours.

[0062] T5, the slurry after ball milling is subjected to spray drying, and the final sample is obtained.

[0063] Comparative Example 2

[0064] T1, preparation of decomposition of the precursor: the urea is calcined at a temperature increasing rate of 12.5°C / min from room temperature to 250°C in a nitrogen atmosphere, and is kept at 250°C for 1 hour.

[0065] T2, decomposition of the precursor: the urea kept at 250°C for 1 hour is continuously calcined at a temperature increasing rate of 13.6°C / min from 250°C to 550-600°C in a nitrogen atmosphere, so that the urea is rapidly decomposed to generate flaky carbon nitride.

[0066] T3, the titanium dioxide is subjected to ultrasonic alkali soaking treatment for 7.8 hours to remove free-state organic matter on the surface of the titanium dioxide and introduce hydroxyl groups.

[0067] T4, the mixture of the carbon nitride and the titanium dioxide at room temperature is placed into a wet ball mill in an air atmosphere, the wet ball mill is operated at 370 r / min for 6 hours.

[0068] T5, the slurry after ball milling is subjected to spray drying, and the final sample is obtained.

[0069] Comparative Example 3

[0070] T1, preparation of decomposition of the precursor: the precursor is calcined at a temperature increasing rate of 3-15°C / min from room temperature to 250°C in a nitrogen atmosphere, and is kept at 250°C for 1 hour, and the precursor can be melamine or urea.

[0071] T2, decomposition of the precursor: the precursor kept at 250°C for 1 hour is continuously calcined at a temperature increasing rate of 3-15°C / min from 250°C to 550-600°C in a nitrogen atmosphere, so that the melamine is rapidly decomposed to generate flaky carbon nitride.

[0072] T3, the obtained carbon nitride is placed into 10 mol / L sodium hydroxide solution, the pressure is kept at 9 MPa, and the duration is 6 hours at a temperature of 60 DEG C.

[0073] T4, the mixture of carbon nitride and titanium dioxide at room temperature is placed into a wet ball mill, the wet ball mill is operated at 30 r / min, and the operation time is 6 hours.

[0074] T5, the slurry after ball milling is spray dried, and the final sample is obtained.

[0075] Hydrogen production data comparison

[0076] Example 1, Example 2, Example 3, Comparative Example 1 (without decomposition preparation of the precursor), Comparative Example 2 (carbon nitride without high pressure treatment group), and Comparative Example 3 (titanium dioxide without alkali soaking treatment group) are tested for hydrogen production capacity, and the testing method is as follows:

[0077] 10 mg of the sample to be tested is accurately weighed into a reactor, 50 mL of triethanolamine aqueous solution with a volume fraction of 20% is added, and ultrasonic dispersion is uniform; the reactor is covered with a quartz upper cover, the reactor is connected to the reaction system, and the temperature of the reaction system is controlled to be 10 DEG C using condensing circulating water; the reaction system is vacuumized to remove air in the pipeline and dissolved oxygen in the solution. Turn on the xenon lamp (power 300 W) for illumination, continuously stir magnetically during the reaction, automatically sample at fixed time intervals, detect the produced hydrogen by gas chromatography thermal conductivity detector, and quantify the produced hydrogen according to the standard curve between peak area and hydrogen molar number. The test data are shown in Table 1:

[0078] Table 1

[0079]

[0080]

[0081] As can be seen from the data in the tables of Example 1, Example 2, Example 3, Comparative Example 1 (without decomposition preparation of the precursor), Comparative Example 2 (carbon nitride without high pressure treatment group), and Comparative Example 3 (titanium dioxide without alkali soaking treatment group), the hydrogen production capacity of the product obtained by the technical scheme is obviously better than that of the products obtained by the comparative examples.

[0082] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a carbon nitride / titanium dioxide composite photocatalyst, characterized by comprising the steps of: The preparation of carbon nitride, the cleaning of titanium dioxide and the catalyst compounding are included. ​ The preparation of carbon nitride includes the following steps: T1, decomposition preparation of the precursor: the precursor is baked from room temperature to 250℃ in nitrogen atmosphere, and is kept for 1-3 hours; T2, decomposition of the precursor: the precursor kept for 1-3 hours is continuously baked from 250℃ to 550-600℃ in nitrogen atmosphere, and is kept for 3-6 hours, then is cooled to room temperature to obtain carbon nitride; T3, high-pressure alkali treatment: the obtained carbon nitride is put into 5-10 mol / L sodium hydroxide solution, and the pressure is kept at 5-10 MPa, and the duration is 6-8 hours at 60℃; The cleaning of titanium dioxide includes the following steps: T1, alkali soaking treatment of titanium dioxide for 6-10 hours; The catalyst compounding includes the following steps: S1, mixing carbon nitride and titanium dioxide in air atmosphere, and baking at 400-500℃ for 1-6 hours, and cooling to room temperature; S2, putting the mixture of carbon nitride and titanium dioxide at room temperature into a wet ball mill in air atmosphere, and the wet ball mill runs at 20-40 r / min for 3-6 hours; S3, spray drying the slurry after ball milling to obtain the final product.

2. The method for preparing a carbon nitride / titanium dioxide composite photocatalyst according to claim 1, characterized by, The precursor includes melamine or urea.

3. The preparation method of the carbon nitride / titanium dioxide composite photocatalyst according to claim 1, characterized in that: In the decomposition preparation of the precursor, the heating rate is 3-15℃ / min; in the decomposition of the precursor, the heating rate is 5-20℃ / min.

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