Preparation method of H-Beta molecular sieve / carbon nitride nanocomposite

Abstract

The application relates to a preparation method of an H-Beta molecular sieve / carbon nitride nanocomposite material, and belongs to the field of semiconductor photocatalysis; the method comprises the following steps: porous super-hydrophilic H-Beta molecular sieve and dicyandiamide are mixed and added into a ball mill jar, the addition amount of the dicyandiamide in the mixture is fixed as 1g, the mixture after ball milling is transferred into a covered crucible after being ball milled for 4 hours, and a g-C3N4 / H-Beta composite photocatalyst is obtained through a high-temperature calcination process.The specific surface area of the prepared g-C3N4 / H-Beta composite photocatalyst is increased by 8.7 times compared with that of a bulk g-C3N4, the active sites exposed on the surface of the photocatalyst are increased, and the diffusion distance of photo-generated charge carriers is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of semiconductor photocatalysis, and particularly relates to a preparation method of H-Beta molecular sieve / carbon nitride nanocomposite. BACKGROUND

[0002] Since entering the 21st century, with the rapid development of human society and the rapid consumption of energy, the two major problems of global non-renewable energy shortage and environmental pollution have become increasingly serious. As a renewable energy, solar energy has attracted much attention due to its huge reserves, green environmental protection and no geographical condition limitation. Photocatalysis technology is a technology for driving redox reactions under light irradiation by using a photocatalyst, which can efficiently and environmentally solve environmental problems and store solar energy in the form of chemical energy without external energy, and has become the most promising green technology in the field of energy and environment. However, the existing technology has the shortcomings of narrow light response range, low solar energy utilization rate and poor photoelectric conversion efficiency, which restricts the improvement of the catalytic activity of the photocatalytic material and its large-scale application in the industrial field.

[0003] Therefore, it is particularly important to develop a visible light responsive photocatalytic material with high photoelectric conversion efficiency. Graphitic carbon nitride (g-C3N4) is a new type of metal-free organic polymer semiconductor photocatalytic material, which has excellent physical and chemical stability and light stability. Its suitable conduction and valence band edge position makes it have strong redox capacity, which can meet the potential requirements of most visible light catalytic reactions. Its production raw materials are cheap and easy to obtain, and the preparation process is simple. It is widely studied and applied in the fields of photocatalytic degradation of organic pollutants and water splitting for hydrogen production. The bulk g-C3N4 is generally prepared by high-temperature thermal polymerization of simple industrial raw materials such as melamine or dicyandiamide. The specific surface area is low, and the exposed active sites are few, which is not conducive to the adsorption and activation of photocatalytic reaction molecules. The poor wettability of bulk g-C3N4 makes it difficult to disperse in the water phase catalytic reaction system, which limits the improvement of its catalytic activity. At the same time, due to its π-electron conjugated system, the recombination rate of photo-generated charge carriers is high, and the migration resistance is large, which makes it difficult to meet the demand of industrial production. SUMMARY

[0004] The application aims to provide a preparation method of H-Beta molecular sieve / carbon nitride nanocomposite, which prepares a graphite phase carbon nitride / H-beta molecular sieve composite by in-situ copolymerization of H-beta molecular sieve and dicyandiamide, improves the specific surface area of the catalyst, and improves the wettability of the catalyst surface to overcome the technical problems in the background art.

[0005] To achieve the above-mentioned purpose, the specific technical scheme of the preparation method of H-Beta molecular sieve / carbon nitride nanocomposite of the application is as follows:

[0006] A method for preparing a H-beta molecular sieve / carbon nitride composite photocatalyst by using H-beta molecular sieve with a contact angle less than 10° as a carrier and growing graphite phase carbon nitride in situ polymerization, the introduction of H-beta molecular sieve increases the specific surface area of the composite catalyst, improves the hydrophilicity, promotes the separation and migration of photo-generated charge carriers, and thus improves the photocatalytic performance.

[0007] A preparation method of a H-Beta molecular sieve / carbon nitride nanocomposite material, comprising the following steps, and the following steps are sequentially performed:

[0008] The porous super-hydrophilic H-beta molecular sieve is mixed with dicyan diamine and added into a ball mill tank, the addition amount of dicyan diamine in the mixture is fixed as 1 g, the ball-milled mixture is transferred to a covered crucible after being sufficiently ball-milled for 4 hours, and a g-C3N4 / H-beta composite photocatalyst is obtained through a high-temperature calcination process.

[0009] Further, the optimal addition amount of H-beta molecular sieve in the composite catalyst is 50 mg, the heating rate in the high-temperature calcination process is set as 10 ℃ / min, the holding temperature is preferably 520 ℃, and the holding time is preferably 2 hours.

[0010] The specific surface area, surface hydrophilicity, separation and migration efficiency of photo-generated charge carriers, and hydrogen production rate of the g-C3N4 / H-beta composite photocatalyst can be adjusted by changing the mass of added H-beta molecular sieve.

[0011] The preparation method of the H-Beta molecular sieve / carbon nitride nanocomposite material has the following advantages:

[0012] 1. The specific surface area of the g-C3N4 / H-beta composite photocatalyst prepared by the method is increased by 8.7 times compared with that of the bulk g-C3N4, the active sites exposed on the surface of the photocatalyst are increased, and the diffusion distance of photo-generated charge carriers is reduced.

[0013] 2. The carrier separation and migration ability of the g-C3N4 / H-beta composite photocatalyst prepared by the method can be adjusted by changing the mass of added H-beta molecular sieve, and the photoelectric conversion efficiency of the catalyst can be optimized.

[0014] 3. When the optimal H-beta molecular sieve addition amount is used in the method, the contact angle is 19.34°, the water molecule adsorption performance is good, and the hydrogen production rate can reach 4.397 mmol·g -1 ·h -1 . BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1TEM images of bulk g-C3N4, H-beta zeolite alone and g-C3N4 / H-beta composite prepared in the embodiment of the present application (a, TEM image of pure g-C3N4; b, TEM image of pure H-Beta zeolite; c, TEM image of g-C3N4 / H-Beta composite; d, high-resolution TEM image of g-C3N4 / H-Beta composite (the lattice fringe spacing of H-Beta zeolite in the composite is shown in the figure)).

[0016] Figure 2 Fourier transform infrared spectrograms of bulk g-C3N4, H-beta zeolite alone and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0017] Figure 3 XRD spectra of bulk g-C3N4, H-beta zeolite alone and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0018] Figure 4 N2 adsorption-desorption curves of bulk g-C3N4 and g-C3N4 / H-beta composite prepared in the embodiment of the present application (a, N2 adsorption-desorption curves of g-C3N4 / H-beta composite and bulk g-C3N4, H-beta zeolite alone; b, pore size distribution curves of g-C3N4 / H-beta composite and bulk g-C3N4, H-beta zeolite alone;).

[0019] Figure 5 Solid-state UV diffuse reflectance spectra of bulk g-C3N4 and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0020] Figure 6 Photoluminescence spectra of bulk g-C3N4 and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0021] Figure 7 Electrochemical impedance spectra of bulk g-C3N4 and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0022] Figure 8 Photocurrent response curves of bulk g-C3N4 and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0023] Figure 9 Contact angles of bulk g-C3N4 and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0024] Figure 10Photocatalytic degradation rate curves of Rhodamine B of bulk g-C3N4, H-beta zeolite alone and g-C3N4 / H-beta composite prepared in the embodiment of the present application.

[0025] Figure 11 Photocatalytic hydrogen production rate curves of bulk g-C3N4, H-beta zeolite alone and g-C3N4 / H-beta composite prepared in the embodiment of the present application. DETAILED DESCRIPTION

[0026] In order to better understand the purpose, structure and function of the present application, the preparation method of the H-Beta zeolite / carbon nitride nanocomposite material of the present application is further described in detail below in combination with the drawings.

[0027] The ambient temperature is 25°C, and the atmospheric pressure is 1 atm.

[0028] Dicyandiamide (C2H2N4) with a molecular weight of 84.08 g / mol;

[0029] Water with a density of 1 g / mL and a molecular weight of 18 g / mol;

[0030] H-beta zeolite, a microporous zeolite, has only pore channels without cages, and is a double six-ring crystal cavity composed of two four-membered rings and four five-membered ring structures.

[0031] Example 1: Preparation of g-C3N4 / H-beta composite

[0032] 25 mg of H-beta zeolite was mixed with 1 g of dicyandiamide in a ball mill jar, and then ball milled in a room temperature planetary ball mill for 4 h. The mixture was then transferred to a 20 mL covered crucible and heated in a muffle furnace at a heating rate of 10°C / min, and then heated to 520°C and kept for 2 hours. The light yellow sample obtained after natural cooling to room temperature was thoroughly ground in an agate mortar, and then washed with ethanol and deionized water for 3 times. The precipitate was dried to obtain a g-C3N4 / H-beta composite photocatalyst.

[0033] As a comparison, bulk g-C3N4 was prepared in the same way as the g-C3N4 / H-beta composite, except that no H-beta zeolite was added.

[0034] Example 2: Preparation of g-C3N4 / H-beta composite

[0035] The mixture of 50 mg of H-beta molecular sieve and 1 g of dicyandiamide was placed in a ball mill tank, and ball milled in a planetary ball mill at room temperature for 4 h. The mixture was then transferred to a 20 mL covered crucible and heated in a muffle furnace at a heating rate of 10 °C / min, and heated to 520 °C for 2 h. The light yellow sample obtained after natural cooling to room temperature was ground thoroughly in an agate mortar, and washed with ethanol and deionized water for 3 times. The precipitate was dried to obtain a g-C3N4 / H-beta composite photocatalyst.

[0036] Example 3: Preparation of g-C3N4 / H-beta composite

[0037] The mixture of 50 mg of H-beta molecular sieve and 1 g of dicyandiamide was placed in a ball mill tank, and ball milled in a planetary ball mill at room temperature for 4 h. The mixture was then transferred to a 20 mL covered crucible and heated in a muffle furnace at a heating rate of 10 °C / min, and heated to 520 °C for 2 h. The light yellow sample obtained after natural cooling to room temperature was ground thoroughly in an agate mortar, and washed with ethanol and deionized water for 3 times. The precipitate was dried to obtain a g-C3N4 / H-beta composite photocatalyst.

[0038] Figure 1 The transmission electron microscopy (TEM) images of the g-C3N4 / H-beta composite prepared in Example 2 of the present application and other materials, wherein a is bulk g-C3N4, b is H-beta molecular sieve alone, c is g-C3N4 / H-beta 50 composite, and d is g-C3N4 / H-beta 50 The high resolution transmission electron microscopy (HRTEM) images of the g-C3N4 / H-beta composite (the lattice fringe spacing of the H-beta molecular sieve in the composite is shown in the figure). As can be seen from the figure, the bulk g-C3N4 exhibits a typical layered structure with a smooth surface; the H-beta molecular sieve alone is almost rhombic with an average diameter of 88.39 nm. After the introduction of the H-beta molecular sieve, the g-C3N4 / H-beta 50 composite exhibits a layered structure similar to that of bulk g-C3N4, and there are crystalline particles in the composite matrix with a lattice edge spacing of 1.27 nm.

[0039] Figure 2 The Fourier transform infrared spectrograms of the g-C3N4 / H-beta composite prepared in Example 2 of the present application and bulk g-C3N4 and H-beta molecular sieve alone. As can be seen from the figure, the absorption peak of g-C3N4 at 804 cm -1 corresponds to the characteristic absorption of the heptazine ring, and the absorption peaks at 1200-1650 cm -1A series of peaks within the range are associated with stretching vibrations of CN or C=N aromatic heterocycles. These peaks are located in the 3000-3500 cm⁻¹ range. -1 The broad absorption bands within the range are due to vibrational peaks of the NH and OH groups on the surface. For H-beta molecular sieves, these peaks are observed at 1250-950, 800-650, and 520-440 cm⁻¹. -1 The peak values ​​in the region were divided into asymmetric stretching, symmetric stretching, and (O-Si-O or O-Al-O) deformation. Characteristic peaks of both g-C3N4 and H-beta molecular sieves were observed, and the synthesized composite material was confirmed to be a g-C3N4 / H-beta composite.

[0040] Figure 3 The XRD patterns of the g-C3N4 / H-beta composite obtained in Example 2 of this invention, as well as the bulk g-C3N4 and the individual H-beta molecular sieve, are shown in the figure. As can be seen from the figure, g-C3N4 exhibits two characteristic diffraction peaks at 13.0° and 27.4°, while the H-beta molecular sieve exhibits two characteristic diffraction peaks at 7.64° and 22.56°. The composite sample g-C3N4 / H-beta... 50 The presence of distinct H-beta molecular sieve and g-C3N4 characteristic peaks confirms the successful preparation of the g-C3N4 / H-beta composite material.

[0041] Figure 4 a represents the N2 adsorption-desorption curves of the g-C3N4 / H-beta complex prepared in Example 2 of this invention, as well as the bulk g-C3N4 and the individual H-beta molecular sieve. Figure 4 Figure b shows the pore size distribution curves of the g-C3N4 / H-beta composite obtained in Example 2 of this invention, as well as the bulk g-C3N4 and the individual H-beta molecular sieve. As can be seen from the figure, g-C3N4 has the lowest specific surface area and pore volume, while the H-beta molecular sieve has the highest. After compositing with H-beta molecular sieve, the g-C3N4 / H-beta... 50 Compared with g-C3N4, the composite material has a significantly increased specific surface area and pore volume, resulting in more active sites, enhanced adsorption capacity of reactants, and improved photocatalytic activity.

[0042] Figure 5 The figures show the solid-state UV diffuse reflectance spectra of the g-C3N4 / H-beta composite and bulk g-C3N4 prepared in Example 2 of this invention. As can be seen from the figures, after compositing with H-beta molecular sieves, the g-C3N4 / H-beta... 50The absorption edge of the composite material is red-shifted to 462 nm compared with g-C3N4. It is shown that the introduction of H-beta molecular sieve can reduce the band gap of g-C3N4, widen the visible light absorption range of the photocatalyst, improve the light absorption capacity, and thus generate more electron-hole pairs, so that the activity of the photocatalyst is greatly improved.

[0043] Figure 6 The photoluminescence spectra of g-C3N4 / H-beta composite prepared in Example 2 of the application and bulk g-C3N4 are shown in the figure. As can be seen from the figure, the high PL emission intensity of g-C3N4 means that the photoelectron recombination rate is relatively high. After the composite H-beta molecular sieve is introduced, the peak intensity is obviously weakened, and the photo-generated carriers have effective recombination inhibition effect.

[0044] Figure 7 The electrochemical impedance spectra of g-C3N4 / H-beta composite prepared in Example 2 of the application and bulk g-C3N4 are shown in the figure. As can be seen from the figure, compared with g-C3N4, the g-C3N4 / H-beta 50 composite material has a lower slope and a certain degree of impedance reduction. It is shown that the introduction of H-beta molecular sieve reduces the internal impedance of g-C3N4 and the migration resistance of carriers.

[0045] Figure 8 The photocurrent response curves of g-C3N4 / H-beta composite prepared in Example 2 of the application and bulk g-C3N4 are shown in the figure. As can be seen from the figure, compared with g-C3N4, the g-C3N4 / H-beta 50 composite material has an increased periodic photocurrent density, which shows that the introduction of H-beta molecular sieve improves the migration ability and generation ability of the photo-excited electrons to different degrees.

[0046] Figure 9 The contact angles of g-C3N4 / H-beta composite prepared in Example 2 of the application and bulk g-C3N4 are shown in the figure. As can be seen from the figure, the hydrophilic H-beta molecular sieve (8.98°) leads to the reduction of the contact angle of the g-C3N4 / H-Beta 50 (19.34°), which is much smaller than that of g-C3N4 (44.10°). It is shown that the hydrophilicity of the composite material synthesized by introducing H-beta molecular sieve is improved, and the g-C3N4 / H-beta 50 composite material has enhanced surface wettability, which is beneficial to its dispersion in the water reaction system, so as to improve the photocatalytic performance.

[0047] Figure 10 The g-C3N4 / H-beta 25The g-C3N4 / H-beta composite prepared in Example 1 50 The g-C3N4 / H-beta composite prepared in Example 2 100 The photocatalytic degradation rate curves of rhodamine B of the g-C3N4 / H-beta composite and bulk g-C3N4 are shown in the figure, and it can be seen from the figure that the degradation rates of all the synthesized g-C3N4 / H-beta photocatalysts are higher than that of g-C3N4, which indicates that the introduction of H-beta zeolite can effectively improve the photocatalytic degradation activity. 50 The degradation rate of the g-C3N4 / H-beta composite prepared in Example 3 is the highest, which is 7.31 times of that of g-C3N4, that is, the optimal content of the composite H-beta zeolite is 50 mg.

[0048] Figure 11 The g-C3N4 / H-beta composite prepared in Example 1 25 The g-C3N4 / H-beta composite prepared in Example 2 50 The g-C3N4 / H-beta composite prepared in Example 3 100 The photocatalytic hydrogen production rate curves of the g-C3N4 / H-beta composite and bulk g-C3N4 are shown in the figure, and it can be seen from the figure that, compared with g-C3N4 (0.696 mmol g -1 h -1 ), the g-C3N4 / H-beta composite material all shows a higher photocatalytic H2 generation rate, which indicates that the introduction of H-beta zeolite can effectively improve the photocatalytic H2 generation activity. 50 The g-C3N4 / H-beta composite prepared in Example 3 shows the highest H2 production (4.397 mmol g -1 h -1 ), which is 6.3 times of that of g-C3N4, and it is concluded that the optimal content of the composite H-beta zeolite is 50 mg.

[0049] It can be seen from the above that, in the method, H-beta zeolite is used as a carrier, and graphite phase carbon nitride is grown by in-situ polymerization to prepare a H-beta zeolite / carbon nitride composite photocatalyst, the introduction of H-beta zeolite increases the specific surface area of the composite catalyst, improves the hydrophilicity, promotes the separation and migration of photo-induced charge carriers, and thus improves the photocatalytic performance.

[0050] It is to be understood that the present application is described by way of example only, and that modifications or alterations can be made to the features and embodiments described without departing from the spirit and scope of the application. In addition, modifications can be made to the features and embodiments described to accommodate specific situations and materials without departing from the spirit and scope of the application. Accordingly, the application is not limited to the specific embodiments disclosed herein, but rather, the scope of the application includes all embodiments falling within the scope of the claims.

Claims

1. A method for improving the photocatalytic performance of graphite phase carbon nitride, characterized in that, The method comprises the following steps, and the steps are sequentially performed: Step S1, H-beta molecular sieve with a contact angle less than 10° is mixed with dicyandiamide and added into a ball mill tank, the amount of dicyandiamide in the mixture is fixed as 1 g, and the mixture is fully ball milled for 4 hours; Step S2, the mixture after ball milling in the step S1 is transferred into a covered crucible, and a high-temperature calcination process is performed; in the step S2, the high-temperature calcination is performed in a muffle furnace and the temperature is increased to 520 ℃; Step S3, the mixture obtained in the step S3 is naturally cooled to room temperature, and a light yellow sample obtained after the natural cooling is fully ground in an agate mortar; Step S4, the mixture after grinding in the step S3 is washed with ethanol and deionized water for multiple times, and a g-C3N4 / H-beta composite photocatalyst is obtained after the precipitate is dried.

2. The method for improving photocatalytic performance of graphite-phase carbon nitride according to claim 1, characterized in that, In the step S1, the optimal amount of H-beta molecular sieve is 20 mg-100 mg.

3. The method for improving photocatalytic performance of graphite-phase carbon nitride according to claim 1, characterized in that, In the step S1, the optimal amount of H-beta molecular sieve is 50 mg.

4. The method for improving photocatalytic performance of graphite-phase carbon nitride according to claim 1, characterized in that, In the step S2, the temperature increasing rate of the high-temperature calcination process is set as 10 ℃ / min.

5. The method for improving the photocatalytic performance of graphite-phase carbon nitride according to claim 1, characterized in that, In the step S2, the holding time of the high-temperature calcination process is 2 hours.

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