Preparation and Application of a Polyheptaazineimide Carbon Nitride Photocatalyst

Abstract

This invention provides a method for preparing a polyheptaazine imide-based carbon nitride photocatalyst and its application, belonging to the field of photocatalytic material preparation technology. The method uses 5-aminotetrazolium as a precursor, a mixture of chloride or bromide salts as a template, a high-temperature solvent, and a structure-directing agent to prepare a polyheptaazine imide-based carbon nitride photocatalyst with a heptaazine crystal phase structure via thermal polymerization. Experiments have shown that this method yields a considerable amount of photocatalyst and exhibits high visible light oxygen production activity, demonstrating potential for photocatalytic water splitting and large-scale industrial application.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic material preparation technology, specifically relating to the preparation of a polyheptaquinone imide carbon nitride photocatalyst and its application in the production of oxygen by splitting water under visible light catalysis. Background Art

[0002] Energy is the material foundation upon which humanity depends for survival and development, and it is also the driving force for sustainable economic and social development. The world's large population and the rapid development of modern industry have led to a continuous increase in human demand for energy, resulting in the over-exploitation of fossil fuels and exacerbating a series of problems such as energy crises and environmental pollution.

[0003] Solar energy conversion for hydrogen production is one of the most ideal and promising green energy acquisition methods. Photocatalytic water splitting for hydrogen production has attracted increasing attention due to its low cost and simple operation. This reaction consists of a hydrogen evolution half-reaction and an oxygen evolution half-reaction. In the oxygen evolution half-reaction, O2 in water molecules... 2- The oxidation of oxygen to a single oxygen molecule by a photocatalyst involves a four-electron transfer, has a high reaction potential, and a slow reaction rate; it is the rate-determining step in the photocatalytic water splitting reaction. Therefore, improving the reaction rate of the oxygen evolution half-reaction in the photocatalyst is one of the key directions for improving the performance of the photocatalytic water splitting reaction. However, very few catalysts with excellent oxygen evolution performance have been found so far, which seriously restricts the research progress of the entire photocatalytic water splitting process.

[0004] Among numerous photocatalysts, carbon nitride, as a novel polymer semiconductor, can exist stably at 600℃. It has advantages such as simple preparation process, low price, response under visible light, and easy structure control. It is considered a promising metal-free semiconductor photocatalyst with certain potential in the field of photocatalytic water splitting. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a polyheptaquinone imide-based carbon nitride photocatalyst and its application. The prepared photocatalyst has a high visible light utilization rate and can achieve a highly efficient water splitting and oxygen production reaction under visible light catalysis.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a polyheptamethine imide carbon nitride photocatalyst, the first technical solution of which is to grind and mix 5-aminotetrazolium as a precursor with a mixed salt template as a high-temperature solvent and structure directing agent, and then synthesize the polyheptamethine imide carbon nitride photocatalyst through a thermal polymerization reaction.

[0008] The second technical solution is to grind and mix 5-aminotetrazole, mixed salt template and cobalt-based precursor, and then synthesize cobalt-doped polyheptamethine imide carbon nitride photocatalyst through thermal polymerization reaction.

[0009] The third technical solution is to grind and mix 5-aminotetrazole, mixed salt template and oxygen-containing precursor, and then synthesize oxygen-doped polyheptaazineimide carbon nitride photocatalyst through thermal polymerization reaction.

[0010] The fourth technical solution is to grind and mix 5-aminotetrazole, mixed salt template, cobalt-based precursor, and oxygen-containing precursor, and then synthesize cobalt-oxygen co-doped polyheptaazineimide carbon nitride photocatalyst through thermal polymerization reaction.

[0011] Furthermore, in the above technical solutions one to four, the mixed salt template is a mixture of potassium chloride or potassium bromide and lithium chloride or sodium chloride, with a mass ratio of 4:6 to 6:4.

[0012] Furthermore, in the above-mentioned technical solutions two and four, the cobalt-based precursor includes cobalt chloride, cobalt nitrate, and cobalt carbonate.

[0013] Furthermore, in the above technical solutions three and four, the oxygen-containing precursor includes oxalic acid and oxalamide.

[0014] Furthermore, in the above technical solutions one to four, the mass ratio of 5-aminotetrazole to the mixed salt template is 1:3 to 1:5.

[0015] Furthermore, in the above-mentioned technical solutions two and four, the mass ratio of the cobalt-based precursor to the mixed salt template is 2:1000-8:1000.

[0016] Furthermore, in the above-mentioned technical solutions three and four, the mass ratio of the oxygen-containing precursor to 5-aminotetrazole is 1:5 to 1:20.

[0017] Furthermore, in the above technical solutions one to four, the grinding time is 0.5 hours.

[0018] Furthermore, in the above technical solutions one to four, the thermal polymerization reaction is carried out under a nitrogen atmosphere, with a nitrogen flow rate of 2-3 L / min, a heating rate of 120-150℃ / h, a reaction temperature of 500-600℃, and a reaction time of 3-6 h.

[0019] The carbon nitride photocatalyst prepared by the above technical solution has a heptaazine crystal phase structure, and its microstructure is a prismatic nanorod with an optical absorption edge around 490 nm.

[0020] The fluorescence intensity of the polyheptamethrinimide carbon nitride photocatalyst obtained in this invention is significantly reduced after doping, and the recombination efficiency of photogenerated carriers generated by photoexcitation is effectively suppressed, giving it a strong oxygen production driving force during photocatalytic reactions. Therefore, it can be used for photocatalytic water splitting to produce oxygen.

[0021] Furthermore, its specific application method is to disperse the prepared polyheptamethrinimide carbon nitride photocatalyst in water, add AgNO3 as an electron sacrificial agent and La2O3 as a pH buffer, and carry out photocatalytic decomposition of water to produce oxygen under light conditions.

[0022] The significant advantages of this invention are:

[0023] (1) In this invention, a mixture of chloride and bromide salts is used as a high-temperature solvent and structure directing agent. By embedding alkali metal potassium ions into the carbon nitride framework, the absorption band edge of the catalyst is effectively improved, and the separation of photogenerated charges is promoted, thereby helping to achieve photocatalytic decomposition to produce oxygen.

[0024] (2) The present invention incorporates oxygen into the carbon nitride framework and / or embeds transition metal cobalt ions into the carbon nitride structure, which effectively inhibits the recombination of photogenerated charges in the photocatalyst, thereby improving its photocatalytic activity in splitting water to produce oxygen.

[0025] (3) The preparation process of this invention is simple, the yield is considerable, the product has high catalytic efficiency, and it has the prospect of large-scale industrial application. Attached Figure Description

[0026] Figure 1 Comparison of powder X-ray diffraction patterns of different polyheptaquinone imide carbon nitride photocatalysts prepared in Examples 1-4.

[0027] Figure 2 Fourier transform infrared spectra of different polyheptaquinone imide carbon nitride photocatalysts prepared in Examples 1-4 are shown.

[0028] Figure 3 The image shows a scanning electron microscope (SEM) image of the polyheptamethine imide carbon nitride photocatalyst prepared in Example 4. a is a top view and b is a cross-sectional view.

[0029] Figure 4 This is a high-resolution transmission electron microscope image of the polyheptamethinimide carbon nitride photocatalyst prepared in Example 4.

[0030] Figure 5 The UV-Vis diffuse reflectance spectrum of the polyheptamethamide carbon nitride photocatalyst prepared in Example 4 and the apparent quantum efficiency diagrams of the photocatalytic decomposition of water to produce oxygen by different polyheptamethamide carbon nitride photocatalysts prepared in Examples 1-4 are shown.

[0031] Figure 6Steady-state fluorescence spectra of different polyheptaquinone imide carbon nitride photocatalysts prepared in Examples 1-4.

[0032] Figure 7 This is a comparison chart showing the photocatalytic activity of different polyheptaquinone imide carbon nitride photocatalysts prepared in Examples 1-4 for oxygen production through water splitting.

[0033] Figure 8 This is a comparison diagram of the photocatalytic oxygen production activity of the polyheptaquinone imide carbon nitride photocatalysts obtained in Example 2 and Comparative Examples 1-2 (a) and Example 4 and Comparative Examples 3-4 (b). Detailed Implementation

[0034] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0035] Example 1

[0036] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride and 2.25 g of lithium chloride, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held at that temperature for 4 h to obtain a polyheptaquinone imide carbon nitride photocatalyst, which was named PHI.

[0037] Example 2

[0038] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride, 2.25 g of lithium chloride, and 0.02 g of cobalt chloride, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held for 4 h to obtain a cobalt-doped polyheptaquinone imide carbon nitride photocatalyst, which was named Co-PHI (i.e., Co...). 0.40 -PHI).

[0039] Example 3

[0040] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride, 2.25 g of lithium chloride, and 0.05 g of oxalic acid, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held at that temperature for 4 h to obtain an oxygen-doped polyheptaquinone imide carbon nitride photocatalyst, which was named O-PHI.

[0041] Example 4

[0042] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride, 2.25 g of lithium chloride, 0.02 g of cobalt chloride, and 0.05 g of oxalic acid, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held for 4 h to obtain a cobalt-oxygen co-doped polyheptaquinone imide carbon nitride photocatalyst, which was named Co / O-PHI (i.e., Co...). 0.40 / O5-PHI).

[0043] Comparative Example 1

[0044] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride, 2.25 g of lithium chloride, and 0.01 g of cobalt chloride, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held at that temperature for 4 h to obtain a cobalt-doped polyheptaquinone imide carbon nitride photocatalyst, which was named Co. 0.20 -PHI.

[0045] Comparative Example 2

[0046] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride, 2.25 g of lithium chloride, and 0.04 g of cobalt chloride, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held at that temperature for 4 h to obtain a cobalt-doped polyheptaquinone imide carbon nitride photocatalyst, which was named Co. 0.80 -PHI.

[0047] Comparative Example 3

[0048] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride, 2.25 g of lithium chloride, 0.02 g of cobalt chloride, and 0.02 g of oxalic acid, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held at that temperature for 4 h to obtain a cobalt-oxygen co-doped polyheptaazineimide carbon nitride photocatalyst, which was named Co. 0.40 / O2-PHI.

[0049] Comparative Example 4

[0050] 1 g of 5-aminotetrazolium was mixed with 2.75 g of potassium chloride, 2.25 g of lithium chloride, 0.02 g of cobalt chloride, and 0.1 g of oxalic acid, and ground for half an hour to obtain a uniform powder. The powder was transferred to a tube furnace and heated to 600 °C at a rate of 120 °C / h under a nitrogen atmosphere at a flow rate of 2 L / min, and held at that temperature for 4 h to obtain a cobalt-oxygen co-doped polyheptaazineimide carbon nitride photocatalyst, which was named Co. 0.40 / O 10 -PHI.

[0051] Figure 1 The figures show a comparison of powder X-ray diffraction (PXRD) spectra of different polyheptaazineimide carbon nitride photocatalysts prepared in Examples 1-4. It can be observed from the figures that all four examples of polyheptaazineimide carbon nitride photocatalysts exhibit two distinct diffraction peaks at 8.1° and 28.2°. The 8.1° peak can be attributed to the diffraction peak of the repeating heptaazine structure within the carbon nitride plane, while the 28.2° peak can be attributed to the interlayer and layered stacking of the heptaazine structure in the graphitic phase of carbon nitride. In addition, a series of weaker diffraction peaks at 14.2°, 21.3°, 32.3°, 35.6°, and 43.5° can be observed. These diffraction peaks all indicate that the prepared photocatalysts are highly crystalline polyheptaazineimide carbon nitride.

[0052] Figure 2 The Fourier transform infrared (FTIR) spectra of the different polyheptaazineimide carbon nitride photocatalysts prepared in Examples 1-4 are shown in the figures. It can be observed from the figures that the carbon nitride photocatalysts of the four examples all have similar spectra. Among them, the spectrum located at 810 cm⁻¹ is particularly noteworthy. -1 915 cm -1 and 995 cm -1 The absorption peaks around the left and right can be attributed to the fingerprint vibration peaks of the heptaazine ring structure in carbon nitride, located at 1200-1700 cm⁻¹. -1 The series of absorption peaks between these peaks can be attributed to the stretching vibrations of the heptaazine ring, as shown in the figure at 3000 cm⁻¹. -1 There is a set of broad but weak peaks nearby, which can be attributed to amino vibrations in the carbon nitride structure.

[0053] Figure 3 This is a scanning electron microscope (SEM) image of the polyheptaquinone imide carbon nitride photocatalyst prepared in Example 4. The image shows that it is a prismatic nanorod solid, with numerous prisms aggregated into a thin sheet of approximately 300 nm.

[0054] Figure 4This is a high-resolution transmission electron microscope (TEM) image of the polyheptaazine imide carbon nitride photocatalyst prepared in Example 4. The image shows that the 0.99 nm spacing lattice fringes correspond to the in-plane repeating stacking of PHI heptaazine structure repeating units, representing the 100 crystal plane of the in-plane heptaazine structure. The 0.30 nm spacing lattice fringes belong to the interlayer spacing of the PHI structure, representing the 002 crystal plane of the heptaazine structure.

[0055] Figure 5 The figures show the UV-Vis diffuse reflectance spectrum of the polyheptaazineimide carbon nitride photocatalyst prepared in Example 4, and the apparent quantum efficiency of the photocatalytic water splitting to produce oxygen by different polyheptaazineimide carbon nitride photocatalysts prepared in Examples 1-4. It can be observed from the figures that the optical absorption edge of Example 4 is around 490 nm, exhibiting a visible light response. Its photocatalytic activity for water splitting to produce oxygen increases with increasing light absorption capacity, and it has a considerable apparent quantum efficiency of approximately 9.0% at 420 nm.

[0056] Figure 6 The steady-state fluorescence spectra of different polyheptaquinone imide carbon nitride photocatalysts prepared in Examples 1-4 are shown. It can be observed from the figures that the fluorescence emission peaks of the carbon nitride photocatalysts in all four examples are located near 500 nm. Among them, PHI has the highest fluorescence emission peak intensity, while Co / O-PHI has the weakest. This indicates that Co / O-PHI has the strongest transport capacity for photogenerated carriers and can effectively promote the separation and migration of photogenerated carriers.

[0057] Oxygen production activity experiment:

[0058] The photocatalytic oxygen production reaction was carried out in a reactor equipped with a 300-watt xenon lamp with a cutoff filter of ≥420 nm, using 50 mg of photocatalyst, 100 mL of deionized water, 1 mmol AgNO3 and 0.6 mmol La2O3.

[0059] Figure 7 This is a comparison chart of the photocatalytic oxygen production activities of different polyheptaazineimide carbon nitride photocatalysts prepared in Examples 1-4. The chart shows that the cobalt-oxygen co-doped polyheptaazineimide carbon nitride photocatalyst prepared in Example 4 achieved a photocatalytic oxygen production rate of 39.68 µmol / h, significantly better than the other photocatalysts.

[0060] Figure 8 This is a comparison graph showing the photocatalytic oxygen production activity of the polyheptaquinone imide carbon nitride photocatalysts obtained in Example 2 and Comparative Examples 1-2(a) and Example 4 and Comparative Examples 3-4(b). The graph shows that the catalyst prepared with a cobalt doping amount of 0.40 wt.% and an oxygen doping amount of 5 wt.% exhibits the best photocatalytic oxygen production activity.

[0061] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a polyheptaazineimide carbon nitride photocatalyst, characterized in that: 5-aminotetrazole, mixed salt template, cobalt-based precursor, and oxygen-containing precursor were ground and mixed, and then thermally polymerized to synthesize cobalt-oxygen co-doped polyheptamethinimide carbon nitride photocatalyst. The mass ratio of 5-aminotetrazole to the mixed salt template is 1:3-1:5; the mass ratio of the cobalt-based precursor to the mixed salt template is 2:1000-8:1000; and the mass ratio of the oxygen-containing precursor to 5-aminotetrazole is 1:5-1:

20. The mixed salt template is a mixture of potassium chloride or potassium bromide and lithium chloride or sodium chloride, with a mass ratio of 4:6 to 6:

4. The cobalt-based precursors include cobalt chloride, cobalt nitrate, and cobalt carbonate; The oxygen-containing precursors include oxalic acid and oxalamide.

2. The method for preparing the polyheptaazineimide carbon nitride photocatalyst according to claim 1, characterized in that: The thermal polymerization reaction is carried out under a nitrogen atmosphere at a temperature of 500-600 °C for 3-6 h.

3. A polyheptaquinone imide carbon nitride photocatalyst prepared by any one of claims 1 to 2, characterized in that: The photocatalyst has a heptaazine crystal phase structure and its microstructure is a prismatic nanorod with an optical absorption edge around 490 nm.

4. The application of the polyheptamethrinimide carbon nitride photocatalyst as described in claim 3 in visible light catalytic water splitting to produce oxygen.

Images