Application of a photocatalyst in photocatalytic air conversion to synthesize nitric acid or nitrate

Abstract

The present invention discloses the use of a photocatalyst for the photocatalytic conversion of air into nitric acid or nitrates. The photocatalyst is monodisperse copper-doped titanium dioxide. This invention is the first to use monodisperse copper-doped titanium dioxide in the field of photocatalytic conversion of air into nitric acid or nitrates. It achieves high efficiency and selectivity in converting air into high-value-added nitric acid or nitrate products under mild conditions. Compared with the current traditional industrial process for the synthesis of nitric acid or nitrates, which requires high temperature, high pressure, and multiple steps of catalytic nitric acid or nitrate synthesis, this application not only simplifies the process flow and reduces reaction costs, but also avoids the use of toxic and hazardous raw materials. Therefore, the application provided by the present invention has high economic and social value.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysis technology, and more specifically to the use of a photocatalyst in the photocatalytic conversion of air into nitric acid or nitrate. Background Art

[0002] Nitric acid and nitrates are important analytical chemical reagents and are widely used in the manufacturing of fertilizers, chemical fibers, and pharmaceuticals. Currently, industrial production typically involves the Haber-Bosch process to produce ammonia, which is then further oxidized under the catalysis of precious metals. However, this traditional process requires harsh reaction conditions such as high temperature and pressure, as well as multiple catalytic conversions. These harsh reaction conditions and complex synthesis processes undoubtedly lead to high energy consumption, high emissions, and high environmental, energy, and cost issues. Theoretically, the use of clean raw materials and green catalytic technologies may offer potential solutions to these problems. The development of nitric acid and nitrate synthesis technologies primarily involves saltpeter, nitrogen, and ammonia. Nitrogen, which can be directly obtained from air, offers excellent sustainability and is a promising alternative to ammonia, the currently widely used raw material in industry. However, nitrogen's inert N≡N bond is very stable, making nitrogen activation technology subject to high energy consumption and low efficiency. Therefore, it is of great significance to provide a low-cost photocatalyst that can efficiently activate and convert air into nitric acid or nitrates under mild conditions. Summary of the Invention

[0003] The object of the present invention is to provide an application of a photocatalyst in the photocatalytic conversion of air into nitric acid or nitrate.

[0004] To achieve the above object, the present invention provides an application of a photocatalyst in the photocatalytic air conversion synthesis of nitric acid or nitrate, wherein the photocatalyst is monodisperse copper-doped titanium dioxide.

[0005] It should be noted that the monodisperse copper of the present invention refers to monodisperse metallic copper atoms, and individual metallic copper atoms have essentially no catalytic activity in the photocatalytic air conversion system for synthesizing nitric acid or nitrates. However, the present invention unexpectedly discovered that doping monodisperse copper into titanium dioxide, using monodisperse copper as active sites and titanium dioxide as a light-absorbing unit, can greatly enhance the ability of titanium dioxide-based photocatalysts to activate nitrogen. Thus, the present invention proposes for the first time the use of monodisperse copper-doped titanium dioxide in the field of photocatalytic air conversion for synthesizing nitric acid or nitrates. Under the synergistic action of the monodisperse copper active component and the titanium dioxide carrier, the goal of efficiently catalytically converting air into nitric acid or nitrates under mild conditions can be achieved.

[0006] Furthermore, in the photocatalyst, the molar ratio of monodisperse copper to titanium dioxide is 0.5 to 6:100, preferably 0.5 to 3:100. When the doping amount of monodisperse copper is within this range, high yield and high selectivity of nitric acid or nitrate can be achieved more effectively.

[0007] Furthermore, the application includes the following steps:

[0008] The photocatalyst is placed in a light-permeable reactor, and air is introduced under light conditions. After the air fully reacts with the photocatalyst, the air is introduced into pure water or water containing cations.

[0009] The above method can adjust the type of cations as needed to obtain nitric acid or different types of nitrates.

[0010] Furthermore, the light is ultraviolet light; preferably ultraviolet light with a wavelength of 350nm to 375nm.

[0011] Furthermore, the intensity of the illumination is at least 160 mW / cm 2 ; preferably not less than 550mW / cm 2 light intensity.

[0012] Furthermore, the cations include H + 、Na + , K + Mg 2+ , Ca 2+ 、Ba 2+ 、Al 3+ 、Fe 2+ 、Fe 3+ 、Zn 2+ 、Cu 2+ 、Ag + One or more of .

[0013] According to a specific embodiment of the present invention, in order to avoid the introduction of nitrates during catalyst synthesis and thus affecting the detection, all raw materials in the synthesis process must not contain nitrates. For example, the resistivity of the pure water can be limited to at least 18.2 MΩ / cm. 2 Eliminate the influence of nitrate.

[0014] Furthermore, the air flow rate is 6-10 mL / min, preferably 8 mL / min. Furthermore, after the photocatalyst is placed in a light-permeable reactor, the process further includes a step of introducing air for purging under light-proof conditions.

[0015] According to a specific embodiment of the present invention, the light-permeable reactor is a flow-through reactor; the flow-through reactor includes an air inlet, an air outlet, and a support body on which a photocatalyst can be placed; the support body has air holes that prevent the catalyst from passing through. For example, the support body can be a metal mesh, a ceramic mesh, or a support body composed of a microfiltration membrane and a sand core support layer. Technicians can fix the support body to a suitable location, such as the middle of the flow-through reactor, as needed, so that air enters through the air inlet, passes through the catalyst, the support body, and finally exits through the air outlet into the absorption tank.

[0016] Furthermore, the preparation method of the photocatalyst comprises the following steps:

[0017] The copper salt and the titanium precursor are mixed and stirred in a solvent, and then synthesized through a hydrothermal reaction.

[0018] Furthermore, the hydrothermal reaction is carried out at 180° C. for 2 to 12 hours.

[0019] Furthermore, the titanium precursor is tetrabutyl titanate or isopropyl titanate.

[0020] According to a specific embodiment of the present invention, the copper salt includes but is not limited to any one of copper chloride, copper sulfate, and copper acetate.

[0021] Furthermore, the molar ratio of the copper salt to the titanium precursor is 0.5 to 6:100.

[0022] According to a specific embodiment of the present invention, the mixing and stirring time is 30 to 60 minutes.

[0023] Furthermore, the solvent is an anhydrous ethanol solution containing hydrofluoric acid. Preferably, the volume ratio of the hydrofluoric acid to the anhydrous ethanol is 1 to 3:40.

[0024] The beneficial effects of the present invention are as follows:

[0025] The present invention is the first to use monodisperse copper-doped titanium dioxide in the field of photocatalytic air conversion to synthesize nitric acid or nitrates, achieving high efficiency and high selectivity in converting air into high-value-added nitric acid or nitrate products under mild conditions. Specifically, the selectivity of nitrate ions is at least 90%.

[0026] Compared to the current traditional industrial process for synthesizing nitric acid or nitrates, which requires high temperature, high pressure, and multiple catalytic steps, the present invention not only simplifies the process flow and reduces reaction costs, but also avoids the use of toxic and hazardous raw materials. Therefore, the application of the present invention has high economic and social value and is expected to be applied in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Figure 1 The transmission electron microscope image and element distribution map of 1% Cu / TiO2 prepared in Example 1 are shown, wherein a shows the transmission electron microscope image of 1% Cu / TiO2; b shows the element distribution map of 1% Cu / TiO2.

[0029] Figure 2 The powder X-ray diffraction patterns of the photocatalysts prepared in Examples 1-4 and Comparative Example 1 are shown.

[0030] Figure 3 A schematic structural diagram of the through-flow reactor of Example 1 is shown.

[0031] Figure 4 The graph shows a comparison of the yield and selectivity of nitrate when the photocatalysts prepared in Examples 1-4 and Comparative Example 1 are used in the photocatalytic conversion of air to synthesize nitric acid or nitrate.

[0032] Figure 5 The graph shows a comparison of the yield of nitrate when the photocatalysts prepared in Example 1 and Examples 5-7 photocatalytically convert air into nitric acid or nitrate under different light intensities.

[0033] Figure 6 A schematic diagram showing the performance cycle stability of the photocatalyst 1% Cu / TiO2 prepared in Example 1. DETAILED DESCRIPTION

[0034] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0035] Example 1

[0036] (1) Provide a monodisperse copper-doped titanium dioxide photocatalyst, the preparation method of which comprises the following steps:

[0037] 1) Add 51.14 mg of CuCl·2H2O and 10 mL of tetrabutyl titanate solution to a 40 mL anhydrous ethanol solution containing 1.5 mL of HF and stir at room temperature for 30 minutes.

[0038] 2) transferring the mixed solution obtained in step 1) into a polytetrafluoroethylene-lined reactor, and then heating the reactor at 180° C. for 12 h to obtain a solid mixture;

[0039] 3) The solid mixture obtained in step 2) was centrifuged and washed three times with ethanol and deionized water, respectively, and dried at 60° C. overnight to obtain monodisperse copper-doped titanium dioxide (wherein the molar ratio of monodisperse copper to titanium dioxide in the catalyst was 1:100, and was recorded as 1% Cu / TiO2).

[0040] (2) subjecting the prepared photocatalyst to air photocatalytic conversion to synthesize nitrate, the specific operation comprising the following steps:

[0041] 100 mg of photocatalyst was spread on the microfiltration membrane in the through-flow reactor, and a N2 / O2 mixture with a volume ratio of 4:1 was blown into the reactor at a rate of 8 mL / min. The mixed gas passed through the catalyst, microfiltration membrane, and sand core from top to bottom, and then was blown into the back of the reactor containing pure water (resistivity 18.2 MΩ / cm 2 ) in the absorption cell, purged for 30 minutes under light-proof conditions, and then used LED light (power 550mW / cm 2 , 365nm ultraviolet light) irradiate the reactor for 1h (the schematic diagram of the through-flow reactor is shown in Figure 3 shown).

[0042] Depend on Figure 1 It can be seen that the overall size of 1% Cu / TiO2 is in the range of 20 to 30 nm, and Cu is doped in titanium dioxide in a monodisperse form.

[0043] Example 2

[0044] The same as Example 1, except that the amount of CuCl·2H2O added was changed to 25.57 mg, and the obtained monodisperse copper-doped titanium dioxide was recorded as 0.5% Cu / TiO2 (wherein the molar ratio of monodisperse copper to titanium dioxide was 0.5:100).

[0045] Example 3

[0046] The same as Example 1, except that the amount of CuCl·2H2O added was changed to 153.42 mg, and the obtained monodisperse copper-doped titanium dioxide was recorded as 3% Cu / TiO2 (wherein the molar ratio of monodisperse copper to titanium dioxide was 3:100).

[0047] Example 4

[0048] The same as Example 1, except that the amount of CuCl·2H2O added was changed to 306.84 mg, and the monodisperse copper-doped titanium dioxide obtained was recorded as 6% Cu / TiO2 (wherein the molar ratio of monodisperse copper to titanium dioxide was 6:100).

[0049] Example 5

[0050] Same as Example 1, except that the light intensity is 160 mW / cm 2 .

[0051] Example 6

[0052] Same as Example 1, except that the light intensity is 290 mW / cm 2 .

[0053] Example 7

[0054] Same as Example 1, except that the light intensity is 420 mW / cm 2 .

[0055] Comparative Example 1

[0056] The same as Example 1, except that pure TiO2 was synthesized without adding CuCl·2H2O, which is recorded as 0% Cu / TiO2.

[0057] Analysis and testing:

[0058] 1) Comparative Example 1-4 and Comparative Example 1 prepared photocatalyst 0.5% Cu / TiO2, 1% Cu / TiO2, 3% Cu / TiO2, 6% Cu / TiO2, 0% Cu / TiO2 X-ray diffraction patterns, such as Figure 2 shown.

[0059] 2) The products obtained in step 2) of Examples 1-4 and Comparative Example 1 were analyzed using anion chromatography of Metrohm. The product yield and nitrate selectivity were as follows: Figure 4 shown.

[0060] The product obtained in step 2) of Example 1, 5-7 was analyzed by anion chromatography using a Swiss Metrohm instrument. The yield of nitrate was as follows: Figure 5 shown.

[0061] 3) The photocatalyst prepared in Example 1 was subjected to the step 2) of Example 1 and the operation was repeated 5 times. The yield of nitrate in each repeated experiment was as follows: Figure 6 shown.

[0062] Depend on Figure 2 It can be seen that there are no obvious Cu particles in the X-ray diffraction pattern, indicating monodisperse doping of Cu, that is, Examples 1-4 have successfully prepared monodisperse copper-doped titanium dioxide.

[0063] Depend on Figure 4It can be seen that (1) the photocatalysts prepared in Examples 1-7 and Comparative Example 1 all showed a certain performance in photocatalytic conversion of air into nitrate, and all showed a high nitrate selectivity (about 90%). However, the photocatalysts in Examples 1-7 synthesized more nitrate under the same conditions, specifically about 1.5-3 times that of pure titanium dioxide. This result shows that the ability of monodisperse copper-doped titanium dioxide to convert air into nitrate is stronger than that of pure titanium dioxide; (2) The doping amount of Cu affects the photocatalytic performance of the photocatalyst. When the molar doping amount of Cu is 1%, the yield of nitrate reaches the highest, reaching 0.93 μmol in 1 h.

[0064] Depend on Figure 5 It can be seen that the stronger the light intensity, the higher the nitrate production.

[0065] Depend on Figure 6 It can be seen that the photocatalyst prepared in Example 1 has high stability and its catalytic performance remains basically unchanged after multiple cycles of use.

[0066] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A photocatalyst for the photocatalytic conversion of air into nitric acid or nitrate, characterized in that: The photocatalyst is monodisperse copper-doped titanium dioxide; The application comprises the following steps: The photocatalyst is placed in a light-permeable reactor, and air is introduced under light conditions. After the air fully reacts with the photocatalyst, the air is introduced into water containing pure water or water containing cations; The air is a N2 / O2 mixed gas with a volume ratio of 4:1; The light is ultraviolet light with a wavelength of 350 nm to 375 nm; the intensity of the light is at least 160 mW / cm 2 ; The method for preparing the photocatalyst comprises the following steps: The copper salt and the titanium precursor are mixed and stirred in a solvent, and then synthesized through a hydrothermal reaction; The hydrothermal reaction is carried out at 180°C for 2 to 12 hours; The molar ratio of the copper salt to the titanium precursor is 0.5 to 6:100; The titanium precursor is tetrabutyl titanate or isopropyl titanate; The solvent is an anhydrous ethanol solution containing hydrofluoric acid; the volume ratio of the hydrofluoric acid to the anhydrous ethanol is 1-3:

40.

2. The use according to claim 1, characterized in that In the photocatalyst, the molar ratio of monodispersed copper to titanium dioxide is 0.5-6:

100.

3. The use according to claim 1, characterized in that The cations include H + 、Na + , K + Mg 2+ , Ca 2+ 、Ba 2+ 、Al 3+ 、Fe 2+ 、Fe 3+ 、Zn 2+ 、Cu 2+ 、Ag + One or more of .

4. The use according to claim 3, characterized in that The air flow rate is 6-10 mL / min.

5. The use according to claim 3, characterized in that After the photocatalyst is placed in a light-transmitting reactor, the method further includes a step of introducing air for purging under light-proof conditions.

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