Hydrophobic carbon nitride photocatalyst with adjustable wettability, preparation method and application thereof

Abstract

The present invention belongs to the field of catalyst technology and relates to a hydrophobic carbon nitride photocatalyst with adjustable wettability, its preparation method, and application. The preparation steps include: adding a cyano compound, an active metal salt, and a template to a solvent for dissolution, freeze-drying, and calcining to produce a single-atom-doped carbon nitride photocatalyst with the template; then, washing away the template and performing a secondary calcination under an NH3 atmosphere. The resulting amino-containing carbon nitride photocatalyst is mixed with an alkyl anhydride in a solvent at a mass ratio of 1:1 to 60, centrifuged, washed, and dried to produce the hydrophobic carbon nitride photocatalyst with adjustable wettability. The present invention uses a cyano compound as a carrier raw material and grafts the alkyl anhydride onto the surface of a carbon material through an acylation reaction of the alkyl anhydride and the amino group, forming a hydrophobic layer of alkyl chains. The catalyst wettability is controlled by adjusting the structure and reaction degree of the alkyl anhydride. The catalyst exhibits excellent catalytic performance in the double-step single-electron reduction of O2 to produce H2O2.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a hydrophobic carbon nitride photocatalyst with adjustable wettability, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is an important chemical that is widely used in food, textile, medicine, chemical and other fields. Commonly used industrial hydrogen peroxide production processes such as the anthraquinone method are not environmentally friendly, the preparation process is not flexible, and the operating cost is high, making it difficult to meet the requirements of green chemistry and sustainable development. Compared with the anthraquinone method, the use of semiconductor photocatalysts to produce hydrogen peroxide through 2e - The direct synthesis of H2O2 from the reduction of O2 has attracted widespread attention due to its environmentally friendly and simple production process. However, from a thermodynamic perspective, O2 reacts more readily to form H2O. H2O2 is only an intermediate product in this reaction and will undergo further hydrogenation or direct decomposition to form H2O, resulting in inefficient O2 utilization and low H2O2 yields. Developing photocatalysts with high H2O2 selectivity and reaction efficiency has become a key and challenging task in H2O2 synthesis research.

[0003] Currently, most research strategies aim to inhibit the side reactions of H2O2 by regulating or influencing the structure and valence state of the reaction center, thereby improving the selectivity and reaction efficiency of H2O2. Although this type of research has made good progress, new regulatory strategies still need to be developed to meet the requirements of industrial applications.

[0004] In recent years, polymer graphite nitride (CN), as a new type of inorganic non-metallic semiconductor photocatalyst responsive to visible light, has been considered as a “sustainable” photocatalytic 2e - Organic semiconductor materials for the reduction reaction (ORR) of H2O2. However, due to the relatively high recombination rate of photogenerated electrons and holes, the photocatalytic activity of CN alone falls far short of expectations. Therefore, the charge transfer kinetics should be optimized to suppress the recombination of photogenerated charges in CN, thereby increasing the migration rate of photogenerated charges from CN to the reaction site. Common strategies for improving the photocatalytic performance of carbon nitride include enhancing light absorption, improving charge separation, and optimizing surface reactions.

[0005] Compared to regulating the reaction center, rapid desorption of unstable H2O2 from the catalyst is equally crucial for improving H2O2 selectivity. Therefore, regulating the wettability of CN photocatalysts is expected to be a new strategy for improving H2O2 selectivity and reaction efficiency. However, there are few reports on regulating the surface wettability of CN materials.

[0006] Among them, document 1 (A. Li, et al., Angew. Chem. Int. Ed. 2019, 10, 14691-14697) used melamine as a precursor and synthesized mesoporous carbon nitride (PCN) by calcination at 550°C; secondly, PCN was modified with a polymer to form a hydrophobic surface (o-PCN), and Pt nanoparticles were loaded onto the o-PCN surface by in situ photodeposition to form Pt / o-PCN; this method reduces the interfacial mass transfer resistance of the reactants and accelerates the reaction kinetics by adjusting the hydrophilicity / hydrophobicity of the PCN photocatalyst. Reference 2 (H. Che, et al., Angew. Chem. Int. Ed. 2021, 11, 25546-25550) reported a novel strategy for synthesizing hydrophilic fragmented carbon nitride (TP-PCN) photocatalysts by utilizing the iodide ion termination polymerization effect. The prepared hydrophilic TP-PCN has abundant edge active sites, which is comparable to the quasi-homogeneous photocatalytic system. Its H2O2 generation rate (3265.4 μM h -1 ) far exceeds other PCN-based photocatalysts; DFT calculations further show that TP-PCN is more conducive to the transition of electrons from spin orbitals to the π* orbitals of O2, thereby optimizing the activation of O2 and reducing the energy barrier for the formation of H2O2; the disadvantage of this method is that the wettability of the PCN photocatalyst cannot be adjusted at high H2O2 generation rates. Reference 3 (W. Yan, et al., Chinese. J. Catal. 2020, 2, 312–321) synthesized a hydrophobic carbon layer by initial wet impregnation and thermal carbonization of glucose, used the prepared C-TiO2 as a catalytic carrier, loaded Pd nanoparticles, and directly synthesized H2O2 from H2 and O2; with the increase of carbon content, the hydrophobicity of the Pd / C-TiO2 surface increased, and the adsorption energy of the catalyst for H2O2 decreased accordingly. The heterogeneous interface regulation engineering of carbon can enhance the interaction between Pd nanoparticles and TiO2, and accelerate the desorption process of H2O2; however, the hydrophobic carbon layer covered the precious metal Pd to a certain extent, resulting in a decrease in the atomic utilization of Pd.

[0007] Based on the above literature research, metal atom-doped carbon nitride and hydrophobic carbon nitride have shown good prospects in the green synthesis application of hydrogen peroxide (H2O2), but the existing synthesis process still has problems such as expensive raw materials and uncontrollable wettability of the prepared catalyst. Summary of the Invention

[0008] The present invention aims to address a series of issues encountered in the prior art for the green synthesis of H2O2. It proposes a hydrophobic carbon nitride photocatalyst with adjustable wettability, its preparation method, and its application. Compared to high-cost supports such as graphene and TiO2, graphite-phase CN derived from cyano compounds offers advantages, including high specific surface area and inexpensive raw materials. The synthesis of hydrophobic carbon nitride photocatalysts using cyano compounds as precursors has broad academic significance and application value in the green synthesis of H2O2.

[0009] The technical solution of the present invention is:

[0010] The present invention uniformly mixes a metal active precursor with a cyano compound, and calcines and carbonizes the mixture at a certain temperature to obtain a single-atom-doped carbon nitride photocatalyst with a template. After suction filtration and washing, the single-atom-doped carbon nitride photocatalyst is obtained. Subsequently, the catalyst is dispersed in acetonitrile, and a certain amount of alkyl anhydride with different carbon chain lengths is added. An acylation reaction is carried out at an appropriate temperature. The acylation reaction of the anhydride and the amino group is grafted onto the catalyst surface to form an alkyl chain hydrophobic layer. The catalyst wettability is regulated by adjusting the structure and reaction degree of the alkyl anhydride. After drying, the final hydrophobic photocatalyst is obtained. In application, the catalyst can efficiently achieve the green synthesis of hydrogen peroxide (H2O2) by adjusting the wettability of the carbon nitride photocatalyst through a two-step single-atom reduction mechanism of oxygen (O2).

[0011] The present invention provides a method for preparing a hydrophobic carbon nitride photocatalyst with adjustable wettability, comprising the following steps:

[0012] (1) adding a cyano compound, an active metal salt, and a template agent in a mass ratio of 1-20:1:20-50 to a solvent, dispersing them by ultrasonication, and freeze-drying them after dissolving;

[0013] In step (1), a cyano compound is dispersed in a solvent and dissolved, and then an active metal salt is added to the solvent and dissolved. The active metal salt and the cyano compound are fully mixed and contacted by ultrasound, and the ultrasound time is 5 to 120 minutes, preferably 10 to 40 minutes. The purpose of ultrasound is to enable the active metal salt and the cyano compound to be fully mixed, so there is no specific time limit, and the ultrasound time can be set according to the experimental arrangement as long as a uniform mixing effect can be achieved. After dissolution, a certain amount of template is added, ultrasonically dispersed, frozen with liquid nitrogen after dissolution, and placed in a freeze dryer for drying.

[0014] The solvent used is any one of water, ethanol, methanol, acetone, toluene and tert-butanol.

[0015] In step (1), the mass ratio of the cyano compound, the active metal salt and the template is any ratio within the range of 1 to 20:1:20 to 50, for example, it can be 1:1:20, 20:1:50, 1:1:50, 20:1:20, 10:1:35, 10:1:20, 10:1:50, 20:1:30 or 20:1:40, etc., or it can be any other ratio within this range.

[0016] (2) calcining the dried solid under an inert atmosphere at 500-580° C. for 0.5-6 h using programmed temperature to obtain a single-atom doped carbon nitride photocatalyst with a template;

[0017] (3) adding water or ethanol to the prepared single-atom-doped carbon nitride photocatalyst with a template, ultrasonicating at 20-45° C. for 5-30 min, stirring for 0.5-3 h to fully mix, then filtering to wash away the template, and drying the obtained solid under inert atmosphere to obtain a single-atom-doped carbon nitride photocatalyst without a template;

[0018] (4) The single-atom-doped carbon nitride photocatalyst prepared in step (3) is subjected to a secondary calcination in an NH3 atmosphere at 300-600°C for 0.5-4h to obtain an amino-containing carbon nitride photocatalyst, and the amino-containing carbon nitride photocatalyst and an alkyl acid anhydride are dispersed in a solvent at a mass ratio of 1:1-60 and uniformly mixed, and heated and stirred at 50-120°C for 0.5-30h. The stirred mixture is centrifuged, washed and dried to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability.

[0019] The mass ratio of the above-mentioned amino-containing carbon nitride photocatalyst to the alkyl anhydride is any ratio within the range of 1:1 to 60, for example, it can be 1:1, 1:5, 1:10, 1:15, 1:20, 1:22, 1:25, 1:28, 1:30, 1:35, 1:38, 1:40, 1:42, 1:45, 1:50, 1:55 or 1:60, etc., or any other ratio.

[0020] The solvent used in step (4) is any one of water, acetonitrile, methanol, ethanol, acetone, cyclohexane, and chloroform, and the detergent used for washing is any one of water, acetonitrile, ethanol, dichloromethane, and acetone;

[0021] The heating temperature in the heating and stirring step is preferably 70 to 100° C., and the time is preferably 20 h or 24 h.

[0022] Furthermore, the alkyl anhydride is selected from alkyl anhydrides of different carbon chain lengths, with the carbon chain length n being 2 to 15; the alkyl anhydride is a hydrophobic reagent, which is grafted onto the surface of the carbon material through the acylation reaction of the anhydride and the amino group to form an alkyl chain hydrophobic layer, and the catalyst wettability is controlled by adjusting the structure and reaction degree of the alkyl anhydride.

[0023] The mass ratio of the amino-rich carbon nitride photocatalyst to the alkyl anhydride is 1:5-25.

[0024] Furthermore, the alkyl anhydride is any one of acetic anhydride, propionic anhydride, valeric anhydride, heptanoic anhydride, octanoic anhydride, nonanoic anhydride, and dodecanoic anhydride.

[0025] Furthermore, the cyano compound is used as a carrier raw material, and the cyano compound is any one or more of cyanamide, dicyandiamide, melamine, and urea;

[0026] The template is one or more of NaCl, NaI and NaBr.

[0027] Furthermore, the active metal salt is in the form of any one of sulfate, acetate, nitrate, and chloride of the active metal component; the active metal component is any one or more of Cu, Co, Mn, Zn, Mg, Ca, and Fe. Preferably, the active metal salt is any one of copper sulfate, copper nitrate, manganese sulfate, magnesium chloride, magnesium acetate, calcium chloride, ferrous acetate, cobalt acetate, or cobalt nitrate.

[0028] Furthermore, the inert atmosphere used for calcination in step (2) is N2 or Ar, and programmed temperature is used during calcination at a heating rate of 0.5 to 10°C / min;

[0029] The carrier raw material used in the present invention is preferably any one of cyanamide, dicyandiamide, melamine or urea. When cyanamide, dicyandiamide or urea is used as the carrier raw material for calcination, the calcination temperature is 550°C; when melamine is used as the carrier raw material, the calcination temperature is 500-580°C, preferably 550°C.

[0030] Preferably, the calcination time in step (2) is 2 to 4 hours.

[0031] The secondary calcination in step (4) adopts programmed temperature increase with a heating rate of 0.5 to 10° C. / min; preferably, the secondary calcination temperature in step (4) is 500 to 580° C. and the calcination time is 2 to 3 hours.

[0032] The present invention also provides a hydrophobic carbon nitride photocatalyst with adjustable wettability, produced using the aforementioned preparation method. The catalyst comprises an active metal component, a support, and a hydrophobic agent. The active metal component is supported on the support in a dispersed state as a single atom. The support is a mesoporous carbon nitride polymer rich in amino groups (-NH2). The hydrophobic agent is an alkyl anhydride of varying carbon chain lengths, which is grafted onto the carbon material surface through an acylation reaction between the anhydride and the amino group, forming an alkyl chain hydrophobic layer. The catalyst's wettability can be controlled by adjusting the structure and reactivity of the alkyl anhydride.

[0033] Furthermore, in the hydrophobic carbon nitride photocatalyst with adjustable wettability, the content of active metal components is 0.1-10 wt%, and the content of alkyl anhydride in the catalyst is 1-60 wt%; preferably, the content of alkyl anhydride is 1-20 wt%.

[0034] The present invention further provides the use of a hydrophobic carbon nitride photocatalyst with adjustable wettability prepared by the above-described preparation method in the synthesis of hydrogen peroxide. The catalyst achieves efficient green synthesis of hydrogen peroxide through a two-step single-atom reduction mechanism of oxygen.

[0035] Beneficial effects of the present invention:

[0036] (1) The present invention uses a mesoporous carbon nitride polymer rich in amino groups (-NH2) derived from a cyano compound as a carrier, and grafts it on the surface of the carbon material through the acylation reaction of alkyl anhydride and amino groups to form an alkyl chain hydrophobic layer. By adjusting the structure and reaction degree of the alkyl anhydride, the catalyst wettability is regulated. The hydrophobic single-atom photocatalyst has excellent catalytic performance in the reaction of preparing H2O2 by two-step single-electron reduction of O2, and exhibits excellent catalytic activity and cyclic stability.

[0037] (2) The preparation method provided by the present invention is universal for different metal elements and can be used to synthesize various single-atom catalysts. The prepared catalysts are low-cost and have excellent performance.

[0038] (3) The hydrophobic single-atom photocatalyst prepared by the present invention can remain inactivated for a long time directly in an air atmosphere, and the catalyst synthesis steps are simple and easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The structural formula of the hydrophobic carbon nitride photocatalyst with adjustable wettability provided by the present invention is: n are alkyl groups of different carbon chain lengths, n ≥ 2, and M is an active metal site;

[0040] Figure 2 This is a spherical aberration electron microscope photograph of catalyst 1# provided in Example 1 of the present invention;

[0041] Figure 3 The contact angles were measured after hydrophobic modification of Cu / CN@NaCl with alkyl anhydrides of different carbon chain lengths.

[0042] Figure 4 This is a comparison chart of H2O2 yields provided for Experimental Example 2. DETAILED DESCRIPTION

[0043] To further understand the present invention, the present invention will be further described below with reference to the accompanying drawings and embodiments, while also providing a clear and complete description of the technical solutions in the embodiments of the present invention. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0044] The present invention provides a hydrophobic carbon nitride photocatalyst with adjustable wettability and a method for preparing the catalyst, comprising the following steps:

[0045] The cyano compound, active metal salt and template agent in a mass ratio of 1 to 20:1:20 to 50 are added to a solvent, ultrasonically dispersed for about 10 minutes to mix them evenly, and after dissolution, they are transferred to a paper cup and placed in a freeze dryer for freeze drying for about 48 hours; the dried solid is transferred to a quartz boat and calcined in a tube furnace under inert atmosphere protection, and the calcination adopts a programmed temperature rise, and the temperature is raised to 500 to 580°C at a rate of 0.5 to 10°C / min, and then cooled after keeping warm for 0.5 to 6 hours to obtain a single-atom doped carbon nitride photocatalyst with a template agent; water or ethanol is then added to the obtained single-atom doped carbon nitride photocatalyst with a template agent solid, and ultrasonicated at a temperature of 20 to 45°C for 5 to 30 minutes, and then stirred for 0.5 to 3 hours, and filtered after being fully mixed. The template is washed by centrifugation with ethanol or water for 2 to 4 times, and the obtained solid is dried in an oven at 60°C under inert atmosphere overnight and ground to obtain a single-atom doped carbon nitride photocatalyst without a template; the solid is then calcined twice in an NH3 atmosphere, and the temperature is raised to 300-600°C at a rate of 0.5-10°C / min and calcined for 0.5-4h to obtain an amino-rich carbon nitride photocatalyst, and the amino-containing carbon nitride photocatalyst and the alkyl anhydride are dispersed in a solvent at a mass ratio of 1:1-40 and uniformly mixed, and heated and stirred at 50-120°C for 0.5-30h. The catalyst mixture solution obtained after the reaction is centrifuged, washed with detergent for 2 to 5 times, and dried in an oven at 80°C overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, whose general structural formula is as follows: Figure 1 shown.

[0046] Application: This catalyst is used in the synthesis reaction of hydrogen peroxide.

[0047] Example 1

[0048] 1.0 g of melamine, 200 mg of copper sulfate, 5 g of NaCl, and 50 mL of methanol were weighed and added to a beaker, ultrasonically dispersed for about 10 minutes to mix evenly, then transferred to a paper cup, and placed in a freeze dryer for freeze drying for 48 hours; the dried solid was transferred to a quartz boat and calcined in a tube furnace under Ar gas atmosphere. The calcination adopted a programmed temperature increase and was heated to 550°C at a rate of 2°C / min. After keeping warm for 2.5 hours, the temperature was lowered to obtain a single-atom-doped carbon nitride photocatalyst with a template; water or ethanol was then added to the obtained single-atom-doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 30°C, ultrasonicated for 15 minutes, stirred for 1.5 hours, filtered after thorough mixing, and washed by centrifugation with ethanol three times to wash away the template. The obtained solid was dried in an oven at 60°C under inert atmosphere overnight and ground to obtain a single-atom-doped carbon nitride photocatalyst without a template, marked as Cu / C-1#;

[0049] Cu / C-1# was calcined twice under NH3 atmosphere, heated to 500℃ at a rate of 2℃ / min and calcined for 2h to obtain an amino-rich carbon nitride photocatalyst, marked as Cu / C-NH3-1#. 60mg Cu / C-NH3-1#, 15mL anhydrous ethanol and 2mL acetic anhydride (the mass ratio of Cu / C-NH3-1# to acetic anhydride is 1:36) were weighed and added to a round-bottom flask, heated in a water bath to 90℃, and stirred for 20h. The catalyst mixture solution obtained after the reaction was centrifuged, washed with acetonitrile 3 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 1#.

[0050] Spherical aberration corrected scanning transmission electron microscopy (AC-STEM) characterization revealed that Cu metal is in a single atomic dispersion state, such as Figure 2 shown.

[0051] Example 2

[0052] Weigh 1.0g of dicyandiamide, 100mg of copper nitrate, 5g of NaCl, and 50mL of ethanol and add them to a beaker. Ultrasonic dispersion is performed for about 10 minutes to mix them evenly. Then, the mixture is transferred to a paper cup and placed in a freeze dryer for freeze drying for 48 hours. The dried solid is transferred to a quartz boat and calcined in a tube furnace. The calcination adopts a programmed temperature increase, and the temperature is increased to 550℃ at a rate of 5℃ / min. After keeping the temperature for 2 hours, the temperature is lowered to obtain a single-atom-doped carbon nitride photocatalyst with a template. Subsequently, water or ethanol is added to the obtained single-atom-doped carbon nitride photocatalyst solid with a template, and the mixture is thoroughly mixed by ultrasonic stirring at 45℃, ultrasonicated for 30 minutes, stirred for 3 hours, filtered after thorough mixing, and washed by centrifugation with ethanol or water 4 times to wash away the template. The obtained solid is dried in an oven at 60℃ under N2 atmosphere overnight, and ground to obtain a single-atom-doped carbon nitride photocatalyst without a template, which is labeled Cu / C-2#.

[0053] Cu / C-2# was calcined twice under NH3 atmosphere, and the temperature was raised to 600℃ at a rate of 5℃ / min and calcined for 4h to obtain an amino-rich carbon nitride photocatalyst, marked as Cu / C-NH3-2#. 60mg Cu / C-NH3-2#, 15mL anhydrous ethanol and 2mL propionic anhydride (mass ratio of 1:33.33) were weighed and added to a round-bottom flask, heated in a water bath to 120℃, stirred for 15h, and the catalyst solution obtained after the reaction was centrifuged, washed with ethanol 3 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 2#.

[0054] Example 3

[0055] 1.0 g of monocyanamide, 60 mg of manganese sulfate, 3 g of NaBr, and 50 mL of tert-butanol were weighed and added to a beaker, ultrasonically dispersed for about 10 minutes to mix evenly, then transferred to a paper cup, and placed in a freeze dryer for freeze drying for 48 hours; the dried solid was transferred to a quartz boat and calcined in a tube furnace under Ar gas atmosphere. The calcination adopted a programmed temperature increase and was heated to 550°C at a rate of 1.0°C / min. After keeping warm for 6 hours, the temperature was lowered to obtain a single-atom-doped carbon nitride photocatalyst with a template; water or ethanol was then added to the obtained single-atom-doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 20°C, ultrasonicated for 10 minutes, stirred for 1 hour, filtered after thorough mixing, and centrifuged and washed 3 times with ethanol or water to wash away the template. The obtained solid was dried in an oven at 60°C under inert atmosphere overnight and ground to obtain a single-atom-doped carbon nitride photocatalyst without a template, marked as Mn / C-3#;

[0056] Mn / C-3# was calcined twice under NH3 atmosphere, and the temperature was raised to 300℃ at a rate of 1℃ / min and calcined for 1h to obtain an amino-rich carbon nitride photocatalyst, marked as Mn / C-NH3-3#. 60mg of Mn / C-NH3-3#, 15mL of anhydrous ethanol and 2mL of valeric anhydride (mass ratio of 1:31.47) were weighed and added to a round-bottom flask, heated in a water bath to 50℃, and stirred for 24h. The catalyst mixture solution obtained after the reaction was centrifuged, washed with water 4 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 3#.

[0057] Example 4

[0058] Weigh 1.0g urea, 100mg magnesium chloride, 3g NaCl and 50mL methanol were added to a beaker and ultrasonically dispersed for about 10 minutes to mix them evenly. The dispersion was then transferred to a paper cup and placed in a freeze dryer for freeze drying for 48 hours. The dried solid was then transferred to a quartz boat and calcined in a tube furnace under N2 atmosphere. The calcination was programmed to heat the temperature at a rate of 10℃ / min to 550℃, kept warm for 3 hours, and then cooled to obtain a single-atom-doped carbon nitride photocatalyst with a template. Water or ethanol was then added to the obtained single-atom-doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 35℃, ultrasonicated for 20 minutes, stirred for 2 hours, filtered after thorough mixing, and centrifuged and washed 4 times with ethanol or water to wash away the template. The obtained solid was dried in an oven at 60℃ under N2 atmosphere overnight and ground to obtain a single-atom-doped carbon nitride photocatalyst without a template, marked as Mg / C-4#.

[0059] Mg / C-4# was calcined twice under NH3 atmosphere, and the temperature was raised to 400℃ at a rate of 10℃ / min for 3h to obtain an amino-rich carbon nitride photocatalyst, marked as Mg / C-NH3-4#. 60mg Mg / C-NH3-4#, 15mL anhydrous ethanol and 2mL heptanoic anhydride (mass ratio of 1:30.77) were weighed and added to a round-bottom flask, heated in a water bath to 90℃, and stirred for 30h. The catalyst solution obtained after the reaction was centrifuged, washed with acetonitrile 5 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 4#.

[0060] Example 5

[0061] 1.0 g of melamine, 500 mg of magnesium acetate, 10 g of NaCl, and 50 mL of methanol were weighed and added to a beaker, ultrasonically dispersed for about 10 minutes to mix evenly, then transferred to a paper cup, and placed in a freeze dryer for freeze drying for 48 hours; the dried solid was transferred to a quartz boat and calcined in a tube furnace under argon atmosphere. The calcination adopted a programmed temperature increase and was heated to 500°C at a rate of 1.5°C / min. After keeping warm for 2.5 hours, the temperature was lowered to obtain a single-atom-doped carbon nitride photocatalyst with a template; water or ethanol was then added to the obtained single-atom-doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 40°C, ultrasonicated for 25 minutes, stirred for 2 hours, filtered after thorough mixing, and centrifuged and washed 3 times with ethanol or water to wash away the template. The obtained solid was dried in an oven at 60°C under inert atmosphere overnight and ground to obtain a single-atom-doped carbon nitride photocatalyst without a template, marked as Mg / C-5#;

[0062] Mg / C-5# was calcined twice under NH3 atmosphere, and the temperature was raised to 500℃ at a rate of 1.5℃ / min and calcined for 2.5h to obtain an amino-rich carbon nitride photocatalyst, marked as Mg / C-NH3-5#. 60mg Mg / C-NH3-5#, 15mL anhydrous ethanol and 2mL nonanoic anhydride (mass ratio of 1:30.5) were weighed and added to a round-bottom flask and mixed evenly. The mixture was heated to 100℃ in a water bath and stirred for 20h. The catalyst solution obtained after the reaction was centrifuged, washed with acetonitrile 3 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 5#.

[0063] Example 6

[0064] Weigh 1.0g melamine, 1.0g calcium chloride, 20.0g NaCl and 50mL methanol were added to a beaker, ultrasonically dispersed for about 10 minutes to mix evenly, then transferred to a paper cup, and placed in a freeze dryer for freeze drying for 48 hours; the dried solid was transferred to a quartz boat and calcined in a tube furnace under Ar or N2 atmosphere protection. The calcination adopted a programmed temperature increase and was heated to 500℃ at a rate of 2℃ / min. After keeping warm for 2.5 hours, the temperature was lowered to obtain a single-atom-doped carbon nitride photocatalyst with a template; water or ethanol was then added to the obtained single-atom-doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 30℃, ultrasonicated for 15 minutes, stirred for 1.5 hours, filtered after thorough mixing, and washed by centrifugation with ethanol 3 times to wash away the template. The obtained solid was dried in an oven at 60℃ under Ar or N2 atmosphere protection overnight, and ground to obtain a single-atom-doped carbon nitride photocatalyst without a template, marked as Ca / C-1#;

[0065] Ca / C-1# was calcined twice under NH3 atmosphere, heated to 600℃ at a rate of 2℃ / min and calcined for 2h to obtain an amino-rich carbon nitride photocatalyst, marked as Ca / C-NH3-1#. 60mg Ca / C-NH3-1#, 15mL anhydrous ethanol and 0.28mL acetic anhydride (mass ratio of 1:5) were weighed and added to a round-bottom flask, heated to 90℃ in a water bath, and stirred for 20h. The catalyst mixture solution obtained after the reaction was centrifuged, washed with acetonitrile 3 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 6#.

[0066] Example 7

[0067] Weigh 1.0g of cyanamide, 50mg of ferrous acetate, 1.0g NaCl and 50mL methanol were added to a beaker, ultrasonically dispersed for about 10 minutes to mix evenly, then transferred to a paper cup, and placed in a freeze dryer for freeze drying for 48 hours; the dried solid was transferred to a quartz boat and calcined in a tube furnace under Ar or N2 atmosphere. The calcination adopted a programmed temperature increase and the temperature was increased to 550℃ at a rate of 2℃ / min. After keeping warm for 2.5 hours, the temperature was lowered to obtain a single-atom-doped carbon nitride photocatalyst with a template; water or ethanol was then added to the obtained single-atom-doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 30℃, ultrasonicated for 15 minutes, stirred for 1.5 hours, filtered after thorough mixing, and washed by centrifugation with ethanol 3 times to wash away the template. The obtained solid was dried in an oven at 60℃ under Ar or N2 atmosphere overnight, and ground to obtain a single-atom-doped carbon nitride photocatalyst without a template, marked as Fe / C-1#;

[0068] Fe / C-1# was calcined twice under NH3 atmosphere, heated to 300℃ at a rate of 2℃ / min and calcined for 2h to obtain an amino-rich carbon nitride photocatalyst, marked as Fe / C-NH3-1#. 60mgFe / C-NH3-1#, 15mL anhydrous ethanol and 1.5mL propionic anhydride (mass ratio of 1:25) were weighed and added to a round-bottom flask, heated to 90℃ in a water bath, stirred for 20h, and the catalyst mixture solution obtained after the reaction was centrifuged, washed with acetonitrile 3 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 7#.

[0069] Example 8

[0070] 2.0 g of dicyandiamide, 100 mg of cobalt acetate, 5.0 g of NaCl, and 50 mL of methanol were weighed and added to a beaker, and ultrasonically dispersed for about 10 minutes to mix them evenly. The mixture was then transferred to a paper cup and placed in a freeze dryer for freeze drying for 48 hours. The dried solid was transferred to a quartz boat and calcined in a tube furnace under Ar or N2 atmosphere. The calcination was performed by programmed temperature rise, and the temperature was raised to 550°C at a rate of 2°C / min. The mixture was kept at this temperature for 2.5 hours and then cooled to obtain a template-containing solid. Single-atom doped carbon nitride photocatalyst; then, water or ethanol was added to the prepared single-atom doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 30°C, ultrasonicated for 15 minutes, stirred for 1.5 hours, and filtered after thorough mixing. The mixture was centrifuged and washed three times with ethanol to remove the template, and the obtained solid was dried in an oven at 60°C under Ar or N2 atmosphere overnight, and ground to obtain a single-atom doped carbon nitride photocatalyst without a template, which was labeled as Co / C-1#;

[0071] Co / C-1# was calcined twice under NH3 atmosphere, heated to 500℃ at a rate of 2℃ / min and calcined for 2h to obtain an amino-rich carbon nitride photocatalyst, marked as Co / C-NH3-1#. 60mg Co / C-NH3-1#, 15mL anhydrous ethanol and 3.8mL valeric anhydride (mass ratio of 1:60) were weighed and added to a round-bottom flask, heated to 90℃ in a water bath, and stirred for 20h. The catalyst mixture solution obtained after the reaction was centrifuged, washed with acetonitrile 3 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 8#.

[0072] Example 9

[0073] 1.0 g of melamine, 200 mg of cobalt nitrate, 8.0 g of NaCl, and 50 mL of methanol were weighed and added to a beaker, ultrasonically dispersed for about 10 minutes to mix evenly, then transferred to a paper cup, and placed in a freeze dryer for freeze drying for 48 hours; the dried solid was transferred to a quartz boat and calcined in a tube furnace under Ar or N2 atmosphere. The calcination was programmed to heat at a rate of 2°C / min to 580°C, kept warm for 2.5 hours, and then cooled to obtain a template-containing solid. Single-atom doped carbon nitride photocatalyst; then, water or ethanol was added to the prepared single-atom doped carbon nitride photocatalyst solid with a template, and the mixture was thoroughly mixed by ultrasonic stirring at 30°C, ultrasonicated for 15 minutes, stirred for 1.5 hours, and filtered after thorough mixing. The mixture was centrifuged and washed three times with ethanol to remove the template, and the obtained solid was dried in an oven at 60°C under Ar or N2 atmosphere overnight, and ground to obtain a single-atom doped carbon nitride photocatalyst without a template, which was labeled as Co / C-1#;

[0074] Co / C-1# was calcined twice under NH3 atmosphere, heated to 400℃ at a rate of 2℃ / min and calcined for 2h to obtain an amino-rich carbon nitride photocatalyst, marked as Co / C-NH3-1#. 60mg Co / C-NH3-1#, 15mL anhydrous ethanol and 0.98mL heptanoic anhydride (mass ratio of 1:15) were weighed and added to a round-bottom flask, heated to 90℃ in a water bath, and stirred for 20h. The catalyst mixture solution obtained after the reaction was centrifuged, washed with acetonitrile 3 times, and dried in an 80℃ oven overnight to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability, marked as 9#.

[0075] Application Example 1

[0076] A certain amount of photocatalyst 1# was placed on a glass slide, and its contact angle was measured to be 45°. In a photoreactor tube, 10 mg of catalyst 1#, 10 mL of isopropanol, and 90 mL of deionized water were added. After ultrasonic dispersion for 10 minutes, the resulting suspension was stirred with oxygen in a dark environment for 30 minutes. After reaching adsorption-desorption equilibrium, a photocatalytic H2O2 synthesis experiment was conducted under a 300 W xenon lamp. The H2O2 generation rate of this catalyst was 748.3 μM h-1. -1 .

[0077] Application Example 2

[0078] A certain amount of photocatalyst 2# was placed on a glass slide, and its contact angle was measured to be 60°. In a photoreactor tube, 10 mg of catalyst 2#, 10 mL of isopropanol, and 90 mL of deionized water were added. After ultrasonic dispersion for 10 minutes, the resulting suspension was stirred with oxygen in the dark for 30 minutes. After reaching adsorption-desorption equilibrium, a photocatalytic H2O2 synthesis experiment was conducted under a 300 W xenon lamp. The H2O2 generation rate of this catalyst was 1136.5 μM h-1. -1 .

[0079] Application Example 3

[0080] A certain amount of photocatalyst 3# was deposited on a glass slide, and its contact angle was measured to be 85.6°. In a photoreactor tube, 10 mg of catalyst 3#, 10 mL of isopropanol, and 90 mL of deionized water were added. After ultrasonic dispersion for 10 minutes, the resulting suspension was stirred with oxygen in a dark environment for 30 minutes. After reaching adsorption-desorption equilibrium, a photocatalytic H2O2 synthesis experiment was conducted under a 300 W xenon lamp. The H2O2 generation rate of this catalyst was 1257.2 μM h-1. -1 .

[0081] Application Example 4

[0082] A certain amount of photocatalyst 4# was deposited on a glass slide, and its contact angle was measured to be 107.6°. In a photoreactor tube, 10 mg of catalyst 4#, 10 mL of isopropanol, and 90 mL of deionized water were added. After ultrasonic dispersion for 10 minutes, the resulting suspension was stirred with oxygen in a dark environment for 30 minutes. After reaching adsorption-desorption equilibrium, a photocatalytic H2O2 synthesis experiment was conducted under a 300W xenon lamp. The H2O2 generation rate of this catalyst was 1347.2 μM h-1. -1 .

[0083] Application Example 5

[0084] A certain amount of photocatalyst 5# was deposited on a glass slide, and its contact angle was measured to be 168.9°. In a photoreactor tube, 10 mg of catalyst 5#, 10 mL of isopropanol, and 90 mL of deionized water were added. After ultrasonic dispersion for 10 minutes, the resulting suspension was stirred with oxygen in a dark environment for 30 minutes. After reaching adsorption-desorption equilibrium, a photocatalytic H2O2 synthesis experiment was conducted under a 300 W xenon lamp. The H2O2 generation rate of this catalyst was 1764.8 μM h-1. -1 .

[0085] Test Example 1

[0086] Alkyl anhydrides of different carbon chain lengths were selected: acetic anhydride (n=2), propionic anhydride (n=3), heptanoic anhydride (n=7), nonanoic anhydride (n=9), and dodecanoic anhydride (n=12). Hydrophobic carbon nitride photocatalysts with adjustable wettability were prepared according to the steps of Example 1. The obtained catalyst powders were then pressed into tablets, and their contact angles were measured using a contact angle meter to obtain the following results: Figure 3 The contact angle is shown.

[0087] from Figure 3 It can be seen from the above that the contact angle of carbon nitride photocatalyst increases gradually with the increase of carbon chain length, which proves that after the acylation reaction between alkyl anhydrides of different carbon chain lengths and carbon nitride photocatalyst, hydrophobic carbon nitride photocatalyst with adjustable wettability can be obtained;

[0088] Test Example 2

[0089] CN@NaCl was used for photocatalytic H2O2 synthesis experiments. Then, copper atoms were doped on the surface of CN@NaCl to obtain Cu / CN@NaCl, and photocatalytic H2O2 synthesis experiments were carried out. Then, alkyl anhydrides with different carbon chain lengths were used to hydrophobically modify Cu / CN@NaCl, and photocatalytic H2O2 synthesis experiments were carried out. The different yields obtained over time were plotted as shown in the figure. Figure 4 shown.

[0090] from Figure 4It can be seen that after metal atoms are doped on the surface of CN@NaCl, the yield of H2O2 is increased by 2 times compared with the original CN@NaCl. After the CN@NaCl with metal active sites, such as Cu / CN@NaCl, is hydrophobically modified, the yield of H2O2 gradually increases with the increase of the carbon chain length of the alkyl anhydride used. When the carbon chain length n=9, the yield of H2O2 is increased by about 5 times compared with the original CN@NaCl. However, when the carbon chain length continues to increase (n=12), the yield of H2O2 decreases. It is speculated that this may be due to the increase in the hydrophobicity of the photocatalyst, which affects the slowdown of the WOR reaction and ultimately leads to a decrease in the yield of H2O2.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, and modifications made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hydrophobic carbon nitride photocatalyst with adjustable wettability for hydrogen peroxide synthesis, characterized in that: The following steps are involved: (1) Adding a cyano compound, an active metal salt, and a template agent in a mass ratio of 1-20:1:20-50 to a solvent, ultrasonically dispersing, dissolving, and freeze-drying; (2) calcining the dried solid under an inert atmosphere at a temperature of 500-580°C for 0.5-6 h to obtain a single-atom doped carbon nitride photocatalyst with a template; (3) Adding water or ethanol to the prepared single-atom-doped carbon nitride photocatalyst with a template, ultrasonicating at 20-45°C for 5-30 min, stirring for 0.5-3 h to fully mix, then filtering to wash away the template, and drying the obtained solid under inert atmosphere to obtain a single-atom-doped carbon nitride photocatalyst without a template; (4) The template-free single-atom doped carbon nitride photocatalyst prepared in step (3) is subjected to a secondary calcination in an NH3 atmosphere at 300-600°C for 0.5-4 h to obtain an amino-containing carbon nitride photocatalyst. The amino-containing carbon nitride photocatalyst and an alkyl anhydride having a carbon chain length n of 2-12 are dispersed in a solvent at a mass ratio of 1:1-60 and uniformly mixed. The mixture is heated and stirred at 50-120°C for 0.5-30 h. The stirred mixture is centrifuged, washed and dried to obtain a hydrophobic carbon nitride photocatalyst with adjustable wettability.

2. The preparation method according to claim 1, characterized in that The mass ratio of the amino-containing carbon nitride photocatalyst to the alkyl acid anhydride is 1:5-25.

3. The preparation method according to claim 2, characterized in that The alkyl anhydride is any one of acetic anhydride, propionic anhydride, valeric anhydride, heptanoic anhydride, octanoic anhydride, nonanoic anhydride, and dodecanoic anhydride.

4. The preparation method according to claim 1, characterized in that The cyano compound is used as a carrier raw material, and the cyano compound is any one or more of cyanamide, dicyandiamide, melamine, and urea; The template is one or more of NaCl, NaI and NaBr.

5. The preparation method according to claim 1, characterized in that The active metal salt is in the form of any one of sulfate, acetate, nitrate and chloride of the active metal component; the active metal component is any one or more of Cu, Co, Mn, Zn, Mg, Ca and Fe.

6. The preparation method according to claim 1, characterized in that The inert atmosphere used for the calcination in step (2) is N2 or Ar, and a programmed temperature is used during the calcination, with a heating rate of 0.5-10°C / min; the secondary calcination in step (4) adopts a programmed temperature, with a heating rate of 0.5-10°C / min.

7. The preparation method according to claim 6, characterized in that The roasting time in step (2) is 2 to 4 hours; the secondary roasting temperature in step (4) is 500 to 580° C., and the roasting time is 2 to 3 hours.

8. A hydrophobic carbon nitride photocatalyst with adjustable wettability obtained by the preparation method according to any one of claims 1 to 7.

9. The hydrophobic carbon nitride photocatalyst with adjustable wettability according to claim 8, characterized in that: The active metal component content in the catalyst is 0.1-10 wt%, and the alkyl anhydride content is 1-60 wt%.

10. Use of the hydrophobic carbon nitride photocatalyst with adjustable wettability obtained by the preparation method according to any one of claims 1 to 7 in the synthesis of hydrogen peroxide.

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