Bimetal nanoparticle reinforced carbon nitride photocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a preparation method and application of a bimetallic nanoparticle reinforced carbon nitride photocatalyst. The preparation method comprises the following steps: firstly, carrying out heat treatment on bulk phase g-C3N4 and urea to obtain a g-C3N4 nanosheet of which the surface contains amino groups and is of a thin-layer structure, then dispersing a bimetallic precursor and a PVP solution into the g-C3N4 nanosheet of which the surface contains amino groups through an equivalent-volume impregnation method, and finally, carrying out plasma reaction of H2 / N2 mixed discharge gas to obtain the g-C3N4 / PVP composite material. And the bimetal nanoparticles are loaded to the surface of g-C3N4. The prepared g-C3N4 has a thin-layer two-dimensional structure, the bimetallic nanoparticles are small in particle size and uniform in dispersion, strong metal-carrier interaction exists between the bimetallic nanoparticles and a carrier, separation and transmission of photo-generated charges can be effectively promoted, surface catalytic reaction is improved, and the g-C3N4 shows extremely excellent photocatalytic hydrogen production performance under visible light.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a bimetallic nanoparticle enhanced carbon nitride photocatalyst and a preparation method and application thereof. Background Art

[0002] As a visible light responsive photocatalyst, graphite carbon nitride (g-C3N4) has attracted much attention due to its suitable energy band structure, simple preparation method, two-dimensional layered structure, and good chemical stability. The two-dimensional layered graphite phase g-C3N4 is stacked together, which is usually called "bulk phase" g-C3N4. However, bulk phase g-C3N4 has shortcomings such as high probability of photogenerated carrier recombination and lack of surface reaction active sites during the photocatalytic reaction, which makes its photocatalytic performance (especially photocatalytic water splitting hydrogen production performance) relatively low.

[0003] Depositing precious metal nanoparticles (such as Pt, Au, Pd, etc.) on the surface of g-C3N4 can inhibit the recombination of photogenerated carriers and increase the active sites for hydrogen production, thereby improving the performance of photocatalytic water splitting to produce hydrogen. Compared with single metal nanoparticles, bimetallic nanoparticles can rely on the synergistic effect of electronic effects (such as ligand effects, stress effects) and localized surface plasmon resonance effects due to the controllability of composition and geometric configuration. By optimizing the interface band structure and carrier transport path, it can effectively broaden the spectral response wavelength range and promote the directional separation and migration of photogenerated electron-hole pairs, thereby significantly improving the quantum efficiency and reaction kinetics of the photocatalytic system.

[0004] Due to the steric hindrance effect of the two-dimensional layered structure of g-C3N4 and the insufficient density of surface exposed active sites, the interface Schottky barrier is not completely constructed when the metal co-catalyst is loaded, resulting in the following technical defects: (1) low degree of overlap of electron orbits at the metal-semiconductor heterojunction; (2) limited spatial separation efficiency of photoinduced carriers; (3) hysteresis of surface interface redox reaction kinetics. In view of the above problems, the present invention introduces amino groups on the surface of thin layer g-C3N4, uses low-temperature plasma to reduce and deposit platinum-based bimetallic nanoparticles on its surface, and constructs atomically dispersed N active sites on the surface of g-C3N4 to achieve precise control of metal-N coordination, construct a Mott-Schottky heterojunction with strong interface coupling characteristics, greatly enhance the photocatalytic hydrogen production performance of g-C3N4, and has important industrial application value for the development of high-efficiency solar energy conversion devices. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, which constructs atomically dispersed N active sites on the surface of g-C3N4 to achieve precise regulation of metal-N coordination, build a Mott-Schottky heterojunction with strong interface coupling characteristics, and greatly enhance the photocatalytic hydrogen production performance of g-C3N4.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, comprising the following steps:

[0007] S1, mixing urea with bulk g-C3N4 and placing in a tube furnace for heat treatment in an air atmosphere to obtain g-C3N4 nanosheets having amino groups on the surface and a thin layer structure;

[0008] S2, dissolving PVP and bimetallic precursors in deionized water, and then dispersing them into g-C3N4 nanosheets having amino groups on the surface by an equal volume impregnation method, and vacuum drying to obtain powder;

[0009] S3. Place the powder obtained in step S2 in a reaction chamber of an inductively coupled low-temperature plasma device, discharge and react in a H2 / N2 mixed atmosphere to load the bimetallic nanoparticles onto the surface of g-C3N4 to obtain a bimetallic nanoparticle-enhanced carbon nitride photocatalyst.

[0010] As a further improvement of the preparation method of bimetallic nanoparticle enhanced carbon nitride photocatalyst:

[0011] Preferably, in step S1, the mass ratio of urea to bulk g-C3N4 is (0.1-1):1, and the two are mixed by grinding; the heat treatment temperature is 480-580°C, the heat treatment time is 1-2h, and the heat treatment heating rate is 5-10°C / min.

[0012] Preferably, the metal precursor in step S2 is a combination of two metal water-soluble salts, and the water-soluble salt is chloride, nitrate, sulfate or sulfite.

[0013] Preferably, one of the bimetallic precursors is a platinum precursor, and the other is a second metal precursor, and the second metal is one of the noble metals Au, Pd, Ag or the non-noble metals Fe, Cu, Co, Ni, Mn, Bi, Al.

[0014] Preferably, the mass ratio of the total amount of metal in the metal precursor in step S2 to the carbon nitride nanosheets containing amino groups on the surface in step S1 is (0.1-1):100.

[0015] Preferably, in step S2, the mass ratio of the total amount of metal in the metal precursor to PVP is 1:(5-20), and after equal volume impregnation, vacuum drying is performed at 60-100°C.

[0016] Preferably, the volume ratio of H2 to N2 in the H2 / N2 mixed atmosphere of step S3 is 3:1.

[0017] Preferably, in step S3, the discharge power of the inductively coupled low-temperature plasma device is 50-200 W, the discharge time is 20-40 min, and the vacuum degree is 5-10 Pa.

[0018] The second object of the present invention is to provide a preparation method as described in any one of the above to prepare a bimetallic nanoparticle-enhanced carbon nitride photocatalyst.

[0019] The third object of the present invention is to provide a use of the above-mentioned bimetallic nanoparticle-enhanced carbon nitride photocatalyst in photocatalytic reactions such as decomposing water to produce hydrogen.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) The present invention provides a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, firstly, bulk g-C3N4 and urea are subjected to heat treatment to obtain g-C3N4 nanosheets containing amino groups on the surface, then a metal precursor and a PVP solution are dispersed into the g-C3N4 nanosheets by equal volume impregnation, and finally the metal precursor is reduced by a low-temperature plasma method to obtain a bimetallic nanoparticle-loaded g-C3N4 composite photocatalyst. Compared with bulk g-C3N4, when a thin layer of g-C3N4 nanosheet is subjected to heat treatment with urea, the steric hindrance effect can be reduced and the degree of surface amination can be increased. Compared with unaminated carbon nitride nanosheets, the carbon nitride nanosheets after amination treatment can construct atomically dispersed N active sites on the surface of g-C3N4, which is conducive to the deposition of metal nanoparticles on its surface. Plasma discharge reduction was carried out in a H2 / N2 mixed atmosphere (the volume ratio of H2 to N2 was 3:1). On the one hand, the volume ratio of H2 to N2 was consistent with the composition of NH3, which could not destroy the amino groups on the surface of g-C3N4 and retain the atomically dispersed N active sites; on the other hand, the H2 plasma could better reduce the metal nanoparticle precursor and load it onto the surface of g-C3N4 nanosheets. Compared with the first metal Pt nanoparticles, the bimetallic nanoparticles can optimize the spectral absorption range, photogenerated carrier separation and migration, and surface catalytic reactions by changing their composition and geometric configuration.

[0022] 2) The bimetallic nanoparticles obtained by the present invention can achieve precise regulation of metal-N coordination. The Mott-Schottky heterojunction with strong interface coupling characteristics between the bimetallic nanoparticles and the g-C3N4 nanosheet carrier can effectively promote the separation and transmission of photogenerated charges, thereby greatly enhancing the photocatalytic hydrogen production performance of g-C3N4. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Pt synthesized in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 0.2 Cu 0.3 Transmission electron microscope image of / g-C3N4.

[0024] Figure 2 The Pt synthesized in Example 1 0.2 Cu 0.3 Transmission electron microscope image of / g-C3N4.

[0025] Figure 3 Pt synthesized in Example 2 0.3 Au 0.2 Transmission electron microscope image of / g-C3N4.

[0026] Figure 4 It is the infrared spectra of g-C3N4 in Example 1, Comparative Example 1 and Comparative Example 2.

[0027] Figure 5 Pt synthesized in Example 1, Comparative Example 4 and Comparative Example 5 0.2 Cu 0.3 XPS spectra of Pt and Cu in / g-C3N4.

[0028] Figure 6 The Pt synthesized in Example 1 and Comparative Example 2 0.2 Cu 0.3 XPS spectrum of N in / g-C3N4.

[0029] Figure 7 The performance of photocatalytic hydrogen production under visible light of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, Comparative Example 7 and Comparative Example 8.

[0030] Figure 8 The Pt synthesized in Example 1 0.2 Cu 0.3 / g-C3N4 photocatalytic hydrogen production stability and hydrogen production rate at different wavelengths.

[0031] Fig. 9 Pt synthesized in Example 2 0.3 Au 0.2 / g-C3N4 photocatalytic hydrogen production stability and hydrogen production rate at different wavelengths.

[0032] Fig.10 The Pt synthesized in Example 4 0.05 Cu 0.05 / g-C3N4 and Pt synthesized in Example 5 0.5 Cu 0.5 / g-C3N4 photocatalytic hydrogen production performance. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, which specifically includes the following steps:

[0036] S1. Weigh 1 g of urea powder and 5 g of bulk g-C3N4 powder in a mass ratio of 0.2:1. Grind and mix them evenly and transfer them into an air muffle furnace. Heat the temperature from room temperature to 500°C at a heating rate of 5°C / min and keep the temperature for 1 hour. After cooling to room temperature, g-C3N4 nanosheets with amino groups on the surface and a thin layer structure are obtained.

[0037] S2, HPtCl6 and Cu(NO3)2 were weighed as bimetallic precursors, HPtCl6 contained 0.2 parts by mass of metal Pt, and Cu(NO3)2 contained 0.3 parts by mass of metal Cu, and the HPtCl6, Cu(NO3)2 and 5 parts by mass of PVP solution were mixed, and then dispersed into 100 parts by mass of g-C3N4 nanosheets containing amino groups on the surface by an equal volume impregnation method, and then vacuum dried at 60°C to obtain powder 1;

[0038] S3, placing powder 1 in the reaction chamber of an inductively coupled low-temperature plasma device, introducing a H2 / N2 mixed gas with a volume ratio of H2 to N2 of 3:1, exhausting the gas in the device, turning on the vacuum pump to evacuate to 5Pa, setting the discharge power to 100W, and the discharge time to 30min. After the discharge, the bimetallic nanoparticles are loaded onto the surface of g-C3N4 to obtain Pt 0.2 Cu 0.3 / g-C3N4 composite photocatalyst.

[0039] Example 2

[0040] This embodiment provides a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, which specifically includes the following steps:

[0041] S1. Weigh 3.2 g of urea powder and 8 g of bulk g-C3N4 powder in a mass ratio of 0.4:1. Grind and mix them evenly and transfer them into an air muffle furnace. Heat the temperature from room temperature to 520°C at a heating rate of 5°C / min and keep the temperature for 1 h. After cooling to room temperature, g-C3N4 nanosheets with amino groups on the surface and a thin layer structure are obtained.

[0042] S2, respectively weighing H2PtCl6 and HAuCl4 as bimetallic precursors, wherein H2PtCl6 contains 0.3 parts by mass of metal Pt, and HAuCl4 contains 0.2 parts by mass of metal Au, mixing H2PtCl6, HAuCl4 and 6 parts by mass of PVP solution, dispersing them into 100 parts by mass of g-C3N4 nanosheets having amino groups on the surface by an equal volume impregnation method, and vacuum drying at 60°C to obtain powder 2;

[0043] S3, placing powder 2 in the reaction chamber of an inductively coupled low-temperature plasma device, introducing a H2 / N2 mixed gas with a volume ratio of H2 to N2 of 3:1, exhausting the gas in the device, turning on the vacuum pump to evacuate to 6Pa, setting the discharge power to 120W, and the discharge time to 40min. After the discharge, the bimetallic nanoparticles are loaded onto the surface of g-C3N4 to obtain Pt 0.3 Au 0.2 / g-C3N4 composite photocatalyst.

[0044] Example 3

[0045] This embodiment provides a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, which specifically includes the following steps:

[0046] S1. Weigh 8 g of urea powder and 10 g of bulk g-C3N4 powder in a mass ratio of 0.8:1. Grind and mix them evenly and transfer them into an air muffle furnace. Heat the temperature from room temperature to 540°C at a heating rate of 10°C / min and keep the temperature for 1.5 h. After cooling to room temperature, g-C3N4 nanosheets with amino groups on the surface and a thin layer structure are obtained.

[0047] S2, respectively weighing H2PtCl6 and AgNO3 as bimetallic precursors, H2PtCl6 containing 0.4 parts by mass of metal Pt, and AgNO3 containing 0.1 parts by mass of metal Ag, mixing H2PtCl6, AgNO3 and 4 parts by mass of PVP solution, dispersing them into 100 parts by mass of g-C3N4 nanosheets containing amino groups on the surface by an equal volume impregnation method, and then vacuum drying at 60°C to obtain powder 3;

[0048] S3, placing powder 3 in the reaction chamber of an inductively coupled low-temperature plasma device, introducing a H2 / N2 mixed gas with a volume ratio of H2 to N2 of 3:1, exhausting the gas in the device, turning on the vacuum pump to evacuate to 8Pa, setting the discharge power to 180W, and the discharge time to 30min. After the discharge, the bimetallic nanoparticles are loaded onto the surface of g-C3N4 to obtain Pt 0.4 Ag 0.1 / g-C3N4 composite photocatalyst.

[0049] In order to better reflect the advantages of the present invention, we compare it with the samples synthesized in the following comparative examples.

[0050] Example 4

[0051] This embodiment provides a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, which specifically includes the following steps:

[0052] S1. Weigh 0.5 g of urea powder and 5 g of bulk g-C3N4 powder in a mass ratio of 0.1:1. Grind and mix them evenly and transfer them into an air muffle furnace. Heat the temperature from room temperature to 480°C at a heating rate of 5°C / min and keep the temperature for 2 h. After cooling to room temperature, g-C3N4 nanosheets with amino groups on the surface and a thin layer structure are obtained.

[0053] S2, respectively weighing H2PtCl6 and Cu(NO3)2 as bimetallic precursors, wherein H2PtCl6 contains 0.05 parts by mass of metal Pt, and Cu(NO3)2 contains 0.05 parts by mass of metal Cu, mixing H2PtCl6, Cu(NO3)2 and 0.5 parts by mass of PVP solution, and dispersing them into 100 parts by mass of g-C3N4 nanosheets having amino groups on the surface by an equal volume impregnation method, and then vacuum drying at 80°C to obtain powder 4;

[0054] S3, placing powder 1 in the reaction chamber of an inductively coupled low-temperature plasma device, introducing a H2 / N2 mixed gas with a volume ratio of H2 to N2 of 3:1, exhausting the gas in the device, turning on the vacuum pump to evacuate to 8Pa, setting the discharge power to 50W, and the discharge time to 40min. After the discharge, the bimetallic nanoparticles are loaded onto the surface of g-C3N4 to obtain Pt 0.05 Cu 0.05 / g-C3N4 composite photocatalyst.

[0055] Example 5

[0056] This embodiment provides a method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, which specifically includes the following steps:

[0057] S1. Weigh 5 g of urea powder and 5 g of bulk g-C3N4 powder in a mass ratio of 1:1. Grind and mix them evenly and transfer them into an air muffle furnace. Heat the temperature from room temperature to 580°C at a heating rate of 5°C / min and keep the temperature for 1 hour. After cooling to room temperature, g-C3N4 nanosheets with amino groups on the surface and a thin layer structure are obtained.

[0058] S2, HPtCl6 and Cu(NO3)2 were weighed as bimetallic precursors, HPtCl6 contained 0.5 parts by mass of metal Pt, and Cu(NO3)2 contained 0.5 parts by mass of metal Cu, and the HPtCl6, Cu(NO3)2 and 20 parts by mass of PVP solution were mixed, and then dispersed into 100 parts by mass of g-C3N4 nanosheets containing amino groups on the surface by an equal volume impregnation method, and then vacuum dried at 60°C to obtain powder 5;

[0059] S3, placing the powder 5 in the reaction chamber of the inductively coupled low-temperature plasma device, introducing a H2 / N2 mixed gas with a volume ratio of H2 to N2 of 3:1, exhausting the gas in the device, turning on the vacuum pump to evacuate to 10Pa, setting the discharge power to 200W, and the discharge time to 20min. After the discharge, the bimetallic nanoparticles are loaded onto the surface of g-C3N4 to obtain Pt 0.5 Cu 0.5 / g-C3N4 composite photocatalyst.

[0060] Comparative Example 1

[0061] This comparative example refers to Example 1, except that: the bulk phase g-C3N4 is not subjected to the amination heat treatment in step S1, and the operations of steps S2 and S3 are directly performed to deposit Pt on the surface of the bulk phase g-C3N4. 0.2 Cu 0.3 Bimetallic nanoparticles.

[0062] Comparative Example 2

[0063] This comparative example refers to Example 1, except that: urea is not added in step S1, the bulk g-C3N4 is directly heat treated, and then Pt is deposited on the surface of the g-C3N4 nanosheets through steps S2 and S3. 0.2 Cu 0.3 Bimetallic nanoparticles.

[0064] Comparative Example 3

[0065] This comparative example refers to Example 1, except that: PVP is not added in the impregnation process of step S2, the metal precursor solution is dispersed into the nanosheets containing amino groups on the surface by an equal volume impregnation method, and then Pt is deposited in step S3. 0.2 Cu0.3 Bimetallic nanoparticles.

[0066] Comparative Example 4

[0067] This comparative example refers to Example 1, except that in step S3, the gas for the plasma discharge reaction is H2.

[0068] Comparative Example 5

[0069] This comparative example refers to Example 1, except that in step S3, the gas for the plasma discharge reaction is N2.

[0070] Comparative Example 6

[0071] This comparative example refers to Example 1, except that: in step S2, a single metal salt H2PtCl6 is used as a metal precursor, and in step S3, only Pt nanoparticles are loaded, and the loading amount of Pt is 0.5 wt%.

[0072] Comparative Example 7

[0073] This comparative example refers to Example 1, except that: in step S2, a single metal salt Cu(NO3)2 is used as a metal precursor, and in step S3, only Cu nanoparticles are loaded, and the loading amount of Cu is 0.5 wt%.

[0074] Comparative Example 8

[0075] This comparative example refers to Example 1, except that the bulk phase g-C3N4 is not processed by steps S1 and S2, and the operation of step S3 is directly performed.

[0076] Photocatalytic water decomposition was used to evaluate the performance of the photocatalysts obtained in the above embodiments and comparative examples under visible light. The light source was a PLS-SXE300D xenon lamp and a UV420 filter (Beijing Bofeilai Technology Co., Ltd.). The gas chromatograph was a Kexiao 1690C model, equipped with a thermal conductivity detector, a FID detector and a methane converter, and the carrier gas was high-purity nitrogen. The steps of the photocatalytic water decomposition hydrogen production reaction are as follows: weigh 5 mg of photocatalyst powder, add it to 100 mL of an aqueous solution containing 20 vol% triethanolamine, stir evenly, and seal the photocatalytic reactor. High-purity nitrogen was introduced to purge the reactor at a flow rate of 50 ml per minute to eliminate the residual gas in the reactor, and then the photocatalytic reaction was started. At regular intervals, the H2 content was analyzed online by a gas chromatograph, and the corresponding apparent quantum efficiency (AQE) was calculated.

[0077] Figure 1 The Pt prepared in Example 1 0.2 Cu 0.3 / g-C3N4 composite photocatalyst and the transmission electron microscope images of the products prepared in Comparative Examples 1, 2 and 3. In Comparative Example 1, the bulk g-C3N4 was not subjected to urea heat treatment and was in an obvious agglomerated state; due to the steric hindrance effect of the bulk g-C3N4 and the lack of surface amination treatment, the synthesized Pt 0.2 Cu 0.3 The average particle size of the nanoparticles reached 4.9 nm, and there was agglomeration (as shown by the circles in the figure). For Comparative Example 2, the bulk g-C3N4 also showed a two-dimensional thin-layer nanosheet structure after heat treatment, but because it was not subjected to surface amino treatment, the synthesized Pt 0.2 Cu 0.3 The average particle size of the nanoparticles reached 2.3 nm. 0.2 Cu 0.3 The particle size distribution of nanoparticles is very uneven, with an average particle size of 3.4 nm, and the agglomeration phenomenon is very serious. In Example 1, Pt 0.2 Cu 0.3 Nanoparticles are uniformly loaded on the surface of g-C3N4 nanosheets, and Pt 0.2 Cu 0.3 There is no agglomeration of nanoparticles and g-C3N4, and the two-dimensional g-C3N4 presents a thin layer structure. 0.2 Cu 0.3 The average particle size of the nanoparticles is only 1.3 nm. It can be seen that the addition of urea to the bulk g-C3N4 after heat treatment and the addition of PVP dispersant has a significant effect on the deposition of Pt 0.2 Cu 0.3 Nanoparticle microstructure has a significant impact.

[0078] Figure 2 The Pt synthesized in Example 1 0.2 Cu 0.3 / g-C3N4 transmission electron microscope image. From the lattice fringe spacing in the figure, it can be seen that the lattice fringe of 0.22nm is between the cubic phase Pt (0.227nm) and Cu (0.209nm), which is consistent with the PtCu alloy structure. The EDS mapping of Pt and Cu also shows that Pt and Cu are uniformly distributed on the surface of g-C3N4 or MC.

[0079] Figure 3 Pt synthesized in Example 2 0.3 Au 0.2 / TEM images of g-C3N4. PtAu nanoparticles are also uniformly loaded on the surface of g-C3N4, with an average particle size of 1.4nm. The lattice fringes of 0.23nm are between the cubic phase Pt (0.227nm) and Au (0.235nm), which is consistent with the PtAu alloy structure. The EDS mapping of Pt and Au also shows that Pt and Au are uniformly distributed on the surface of g-C3N4 or MC.

[0080] Figure 4 The Pt prepared in Example 1 0.2 Cu 0.3 Infrared spectra of the final products synthesized by / g-C3N4 composite photocatalyst and Comparative Example 1 and Comparative Example 2. 2800-3400cm -1 The broad peak at corresponds to the NH bond vibration on the surface of g-C3N4, that is, the degree of surface amination. For Comparative Examples 1 and 2, the transmittance of NH bond vibration is about 78%, indicating that g-C3N4 has not been surface amination-modified and its surface amination degree is very weak. For Example 1, the transmittance of NH bond vibration is about 72%, which is significantly lower than that of Comparative Examples 1 and 2, indicating that a large number of amino groups are introduced on the surface of g-C3N4.

[0081] Figure 5 The Pt prepared in Example 1 0.2 Cu 0.3 XPS spectra of Pt and Cu in the final products synthesized by the composite photocatalyst of g-C3N4 and Comparative Examples 4 and 5. According to the XPS spectra of Pt 4f, for the Pt synthesized in Comparative Example 5 0.2 Cu 0.3 Nanoparticles, since the plasma discharge gas is N2, the synthesized Pt is mainly in an oxidized state (Pt 2+ and Pt 4+ ), metallic Pt 0 The proportion of Pt is relatively low (19.8%), indicating that it is difficult for N2 plasma to remove Pt 4+ Reduction to metallic Pt 0 For the Pt synthesized in Example 1 and Comparative Example 4 0.2 Cu 0.3 Nanoparticles, due to the H2 plasma in the discharge gas, Pt 4+ Almost all of them are reduced to metallic Pt 0 According to the binding energies of Pt 4f and Cu 2p in the figure, compared with Comparative Example 5, the binding energies of Pt 4f in Example 1 and Comparative Example 4 are red-shifted, while the binding energies of Cu 2p are blue-shifted. This is because 0.2 Cu 0.3In the nanoparticles, the introduction of the second metal Cu leads to charge rebalance, and there is a migration of photogenerated charges from Pt to Cu. Compared with Comparative Example 4, Pt 4f in Example 1 has a larger binding energy, while Cu 2p has a smaller binding energy, indicating that the Pt synthesized in Example 1 0.2 Cu 0.3 / g-C3N4 has a strong metal-support interaction. This can be seen from Figure 6 The XPS spectrum of N1s further proves that. Compared with Comparative Example 4, N1s in Example 1 also has a greater binding energy. This is because in Example 1, plasma discharge reduction is carried out in a H2 / N2 mixed atmosphere (the volume ratio of H2 to N2 is 3:1). On the one hand, the volume ratio of H2 to N2 is consistent with the composition of NH3, which can not destroy the amino groups on the surface of g-C3N4 and retain the atomically dispersed N active sites; on the other hand, H2 plasma can better reduce the metal nanoparticle precursor and load it onto the surface of g-C3N4 nanosheets. Therefore, Example 1 can achieve precise control of metal-N coordination and construct a Mott-Schottky heterojunction with strong interface coupling characteristics, which is very beneficial to the improvement of photocatalytic performance.

[0082] Figure 7 The Pt prepared in Example 1 0.2 Cu 0.3 The performance of the final products obtained by photocatalytic hydrogen production under visible light by using the composite photocatalyst of g-C3N4 and comparative examples 1, 2, 3, 4, 5, 6, 7 and 8. The photocatalytic hydrogen production rate of bulk g-C3N4 without any treatment was only 0.72 mmol h -1 g -1 After the noble metals were deposited on the surface of g-C3N4, the performance of photocatalytic hydrogen production was significantly improved. For Comparative Example 1, the bulk g-C3N4 was directly deposited with Pt without urea heat treatment. 0.2 Cu 0.3 Nanoparticles, the hydrogen production rate increased to 31.1mmol h -1 g -1 For comparative example 2, the bulk g-C3N4 was heat treated and then Pt was deposited. 0.2 Cu 0.3 Nanoparticles can increase the hydrogen production rate to 42.6 mmol h -1 g -1 For Comparative Example 3, Pt synthesized without adding PVP dispersant 0.2 Cu 0.3 / g-C3N4, and its hydrogen production rate is 78.4mmol h - 1 g -1Although Pt in Comparative Example 3 0.2 Cu 0.3 The nanoparticles have uneven particle size distribution and serious agglomeration, but still show better activity than Comparative Examples 1 and 2. 0.5 / g-C3N4 and Cu synthesized in Comparative Example 7 0.5 / g-C3N4, the photocatalytic hydrogen production rates were 61.9 and 21.3 mmol h -1 g -1 For the Pt synthesized in Comparative Examples 4 and 5 0.2 Cu 0.3 / g-C3N4, and their hydrogen production rates were 119.8 and 96.3 mmol h -1 g -1 For the Pt synthesized in Example 1 of the present invention 0.2 Cu 0.3 / g-C3N4 showed the highest photocatalytic hydrogen production performance, with a hydrogen production performance of 229.6mmol h -1 g -1 , which are 7.4, 5.4, 2.9, 1.9, 2.4, 3.7, 10.8 and 318.9 times of those in Comparative Examples 1, 2, 3, 4, 5, 6, 7 and 8, respectively. It can be seen that the surface amination treatment, the addition of PVP dispersant and the selection of H2 / N2 mixed discharge gas have a significant effect on the synthesized Pt 0.2 Cu 0.3 / g-C3N4 has a significant impact on the photocatalytic performance.

[0083] Figure 8 The Pt synthesized in Example 1 0.2 Cu 0.3 / g-C3N4 photocatalytic hydrogen production stability and hydrogen production rate at different wavelengths. It can be seen from the figure that Pt 0.2 Cu 0.3 / g-C3N4 showed good photocatalytic stability under visible light. After 4 rounds of reaction for 24 h, the performance of photocatalytic hydrogen production did not change significantly. The hydrogen production rates at 435 nm, 450 nm, 475 nm, 500 nm and 520 nm were 72.6, 39.4, 15.8, 6.1 and 1.2 mmol h, respectively. –1 g –1 , the corresponding AQEs are 30.2%, 15.2%, 4.1%, 1.4% and 0.26% respectively. 0.2 Cu 0.3 / g-C3N4, after being loaded with the second metal Cu, not only the Pt content was greatly reduced, but also its photocatalytic hydrogen production performance was significantly improved, with the AQE at 435nm reaching 30.2%.

[0084] Fig. 9 Pt synthesized in Example 2 0.3 Au 0.2 / g-C3N4 photocatalytic hydrogen production stability and hydrogen production rate at different wavelengths. 0.2 Cu 0.3 Compared with g-C3N4, the Pt synthesized in Example 2 0.3 Au 0.2 / g-C3N4 has higher photocatalytic hydrogen production performance, and the hydrogen production rate reaches 249.8mmol h -1 g -1 The photocatalytic efficiency was 82.4, 57.6, 91.1, 37.3, 9.1, 2.7 and 0.8 mmol h at 435 nm, 450 nm, 475 nm, 500 nm, 520 nm, 550 nm and 600 nm, respectively. –1 g –1 , and the corresponding AQEs are 34.3%, 22.2%, 23.8%, 8.2%, 1.9, 0.6 and 0.15%, respectively. 0.2 Cu 0.3 Compared with g-C3N4, the Pt synthesized in Example 2 0.3 Au 0.2 The AQE of / g-C3N4 at 435nm and 475nm reached 34.3% and 23.8% respectively, and the maximum response wavelength reached 600nm, which is mainly due to the surface plasmon resonance effect of nano-Au.

[0085] Similarly, the Pt 0.05 Cu 0.05 / g-C3N4 and Pt prepared in Example 5 0.5 Cu 0.5 / g-C3N4 composite photocatalyst was used for photocatalytic hydrogen production test, and the hydrogen production rates were 141.2 and 172.3 mmol h -1 g -1 ,like Fig.10 Compared with all comparative examples, the Pt 0.05 Cu 0.05 / g-C3N4 and Pt 0.5 Cu 0.5 / g-C3N4, still shows good photocatalytic hydrogen production performance.

[0086] Those skilled in the art should understand that the above are only some specific embodiments of the present invention, rather than all embodiments. It should be noted that for those of ordinary skill in the art, many modifications and improvements can be made, and all modifications or improvements that do not exceed the scope of protection of the present invention should be regarded as.

Claims

1. A method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst, characterized in that: The following steps are involved: S1, mixing urea with bulk g-C3N4 and placing in a tube furnace for heat treatment in an air atmosphere to obtain g-C3N4 nanosheets having amino groups on the surface and a thin layer structure; S2, dissolving PVP and bimetallic precursors in deionized water, and then dispersing them into g-C3N4 nanosheets having amino groups on the surface by an equal volume impregnation method, and vacuum drying to obtain powder; S3. Place the powder obtained in step S2 in a reaction chamber of an inductively coupled low-temperature plasma device, discharge and react in a H2 / N2 mixed atmosphere to load the bimetallic nanoparticles onto the surface of g-C3N4 to obtain a bimetallic nanoparticle-enhanced carbon nitride photocatalyst.

2. The method for preparing the bimetallic nanoparticle enhanced carbon nitride photocatalyst according to claim 1, characterized in that: In step S1, the mass ratio of urea to bulk g-C3N4 is (0.1-1):1, and the two are mixed by grinding; the heat treatment temperature is 480-580°C, the heat treatment time is 1-2h, and the heat treatment heating rate is 5-10°C / min.

3. The method for preparing the bimetallic nanoparticle enhanced carbon nitride photocatalyst according to claim 1, characterized in that: In step S2, the metal precursor is a combination of two metal water-soluble salts, and the water-soluble salt is chloride, nitrate, sulfate or sulfite.

4. The method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst according to claim 1 or 3, characterized in that: One of the bimetallic precursors is a platinum precursor, and the other is a second metal precursor, wherein the second metal is one of the noble metals Au, Pd, Ag or the non-noble metals Fe, Cu, Co, Ni, Mn, Bi, Al.

5. The method for preparing the bimetallic nanoparticle enhanced carbon nitride photocatalyst according to claim 1, characterized in that: The mass ratio of the total amount of metal in the metal precursor in step S2 to the carbon nitride nanosheets containing amino groups on the surface in step S1 is (0.1-1):

100.

6. The method for preparing a bimetallic nanoparticle-enhanced carbon nitride photocatalyst according to claim 1 or 5, characterized in that: In step S2, the mass ratio of the total amount of metal in the metal precursor to PVP is 1:(5-20), and after equal volume impregnation, vacuum drying is performed at 60-100°C.

7. The method for preparing a bimetallic nanoparticle enhanced carbon nitride photocatalyst according to claim 1, characterized in that: The volume ratio of H2 to N2 in the H2 / N2 mixed atmosphere of step S3 is 3:

1.

8. The method for preparing a bimetallic nanoparticle enhanced carbon nitride photocatalyst according to claim 1, characterized in that: In step S3, the discharge power of the inductively coupled low-temperature plasma device is 50-200W, the discharge time is 20-40min, and the vacuum degree is 5-10Pa.

9. A bimetallic nanoparticle-reinforced carbon nitride photocatalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the bimetallic nanoparticle-enhanced carbon nitride photocatalyst according to claim 9 in a photocatalytic reaction.

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