Photocatalyst of carbon-nitrogen coated transition metal cluster and preparation method and application thereof

Abstract

The present application relates to the field of photocatalyst, discloses a carbon and nitrogen coated transition metal cluster photocatalyst and its preparation method and application, the method comprises the following steps: in the presence of organic solvent, mixing transition metal nitrate and diamino maleonitrile, then the mixture is hydrothermally reacted to obtain a solid product; the transition metal nitrate is selected from at least one of cobalt nitrate, iron nitate and copper nitrate; the molar ratio of transition metal nitrate and diamino maleonitrile is 1:1-3; the hydrothermal reaction conditions include: temperature is 120-140 DEG C, time is 8-15h; under the protection of inert gas, the solid product is calcined, and then the calcined product is pickled; the calcination conditions include: the temperature rising rate is 3-10 DEG C / min, the temperature is 450-700 DEG C, and the time is 1-4h. The photocatalyst obtained by the method can catalyze the production of hydrogen peroxide and catalyze 1,5-dihydroxynaphthalene oxidation to produce juglone, and the yield of the product is higher.

Description

Technical Field

[0001] This invention relates to the field of photocatalysts, specifically to photocatalysts with carbon and nitrogen-coated transition metal clusters, their preparation methods, and applications. Background Technology

[0002] Molecular oxygen ( 3 O2 is a mild, clean, and inexpensive oxidant; however, it is difficult for it to directly and rapidly initiate chemical reactions under environmental conditions. 3 O2 is converted into reactive oxygen species (ROS), such as... 1 O2、·O2 － ·OH, H2O2, etc., can enhance the interaction between them and the substrate, thereby accelerating the reaction process.

[0003] H2O2, as an environmentally friendly oxidant, is widely used not only in green chemistry (synthesis of inorganic, organic, and fine chemicals) and environmental protection (medical disinfection, wastewater treatment), but is also emerging as a new clean energy source. Currently, industrial H2O2 production is still mainly based on the anthraquinone process. While this method produces high concentrations of H2O2, it also exposes several hidden dangers. First, the process itself involves many purification steps, which are cumbersome and consume large amounts of electricity and raw materials at each step. Second, the production process uses large amounts of hydrogen, posing high safety risks. Photocatalysis... 3 The reduction of O2 to H2O2 is gaining close attention from researchers worldwide due to its safety, environmental friendliness, simplicity, and economy. It uses only oxygen and water, and can achieve highly selective preparation of H2O2 under the influence of light and a catalyst, reducing both the risk of explosion and the costs of product handling, transportation, and storage.

[0004] 1,5-Dihydroxynaphthalene (1,5-DHN) is a key dye intermediate, primarily used in the production of acid mordant dyes. It boasts rich color payoff, good fastness, and low cost, holding a significant position in the dye industry. However, some enterprises with outdated dyeing processes have failed to achieve complete conversion of 1,5-dihydroxynaphthalene, resulting in some of it being discharged into production wastewater. 1,5-Dihydroxynaphthalene is highly irritating and toxic, not only polluting the environment but also potentially causing malformations and cancer in plants and animals if it seeps into sewage systems. Related studies have found that… 1O2 can selectively oxidize 1,5-dihydroxynaphthalene to juglone. Juglone is an aromatic compound with a quinone structure isolated from the pericarp, leaves, and bark of some species in the Juglandaceae family. It has been widely researched and applied in the fields of medicine, biology, and chemistry. It can kill tumor cells by inhibiting DNA synthesis in tumor cells through cell cycle regulation; inhibit cell differentiation by disrupting ion channels in bacterial cell membranes and hindering transmembrane transport; regulate immune function to maintain the balance of the human immune system; and enter certain plants to produce toxic effects, thereby eliminating pests and weeds. It is a novel, pollution-free plant-derived pesticide. The directed oxidation of 1,5-dihydroxynaphthalene under room temperature, air, and light conditions transforms environmental pollutants into high-value-added chemicals, not only turning waste into treasure but also providing new ideas for the artificial synthesis of natural plant extracts.

[0005] Currently, the photocatalytic production of hydrogen peroxide from oxygen still faces several challenges. First, the photocatalyst structure is not sufficiently stable; prolonged light exposure can corrode the material surface. Strong acid / alkaline systems alter the chemical environment of the material surface. Furthermore, the generated H2O2 is a strong oxidizing agent, easily damaging the catalyst's morphology, pore structure, surface active sites, and even its internal chemical structure during the reaction. Second, the photoreactivity of the photocatalyst is insufficient. The energy level mismatch between the excited states generated after photoexcitation prevents efficient transfer of absorbed light energy between triplet and singlet excited states. An unsuitable bandgap structure affects the separation and migration of photogenerated carriers, limiting the material's light absorption range, reducing light energy utilization, and decreasing H2O2 production. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low hydrogen peroxide yield and low juglone yield in the process of catalytic production of hydrogen peroxide and catalytic oxidation of 1,5-dihydroxynaphthalene to juglone, and to provide a photocatalyst with carbon and nitrogen coated transition metal clusters, its preparation method and application.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a photocatalyst with carbon and nitrogen-coated transition metal clusters, the preparation method comprising:

[0008] (1) In the presence of an organic solvent, a transition metal nitrate is mixed with a diaminomaleitrile, and the resulting mixture is then subjected to a hydrothermal reaction to obtain a solid product; wherein:

[0009] The transition metal nitrate is selected from at least one of cobalt nitrate, ferric nitrate, and copper nitrate;

[0010] The molar ratio of the transition metal nitrate to the diaminomaleitrile is 1:1-3;

[0011] The conditions for the hydrothermal reaction include: a hydrothermal temperature of 120-140℃ and a hydrothermal time of 8-15h.

[0012] (2) Under inert gas protection, the solid product is calcined, and then the calcined product is acid-washed; wherein:

[0013] The calcination conditions include: a heating rate of 3-10℃ / min, a calcination temperature of 450-700℃, and a calcination time of 1-4h.

[0014] A second aspect of the present invention provides a carbon-nitrogen-coated transition metal cluster photocatalyst prepared by the method for preparing a carbon-nitrogen-coated transition metal cluster photocatalyst as described in the first aspect. The photocatalyst comprises a transition metal cluster and a nitrogen-doped carbon layer coated on the surface of the transition metal cluster. The transition metal in the transition metal cluster is selected from at least one of cobalt, iron, and copper. As measured by X-ray photoelectron spectroscopy, the mass fraction of the transition metal in the photocatalyst is 1-5%, the mass fraction of nitrogen is 15-25%, and the mass fraction of carbon is 70-80%.

[0015] A third aspect of this invention provides the application of the carbon-nitrogen-coated transition metal cluster photocatalyst described in the second aspect in the photocatalytic production of hydrogen peroxide, the application comprising:

[0016] The photocatalyst was dispersed in an aqueous sulfuric acid solution to obtain a dispersion. Air was then introduced into the dispersion and continuously bubbled. The bubbled dispersion was then subjected to a reduction reaction under light irradiation to obtain hydrogen peroxide.

[0017] A fourth aspect of this invention provides the application of the carbon-nitrogen-coated transition metal cluster photocatalyst described in the second aspect in the photocatalytic oxidation of 1,5-dihydroxynaphthalene to juglone, the application comprising:

[0018] The dispersion containing the solvent and the photocatalyst was mixed with 1,5-dihydroxynaphthalene under stirring to obtain a mixture, which was then reacted under light to obtain juglone.

[0019] Through the above technical solution, the photocatalyst and its preparation method for carbon-nitrogen coated transition metal clusters provided by the present invention have the following advantages:

[0020] The preparation method provided by this invention utilizes inexpensive raw materials diaminomaleitrile and transition metal nitrates through hydrothermal reaction, calcination, and acid washing to obtain a carbon-nitrogen-coated transition metal cluster photocatalyst. The photocatalyst comprises transition metal clusters and a nitrogen-doped carbon layer coating the surface of the transition metal clusters. The transition metal in the transition metal clusters is selected from at least one of cobalt, iron, and copper. X-ray photoelectron spectroscopy analysis shows that the mass fraction of the transition metal in the photocatalyst is 1-5%, the mass fraction of nitrogen is 15-25%, and the mass fraction of carbon is 70-80%. The preparation method is simple and low-cost.

[0021] The carbon-nitrogen-coated transition metal cluster photocatalyst provided by this invention can effectively resist light irradiation, acid / alkali corrosion, and H2O2 oxidation, thereby maintaining the catalyst's structure and the activity of reaction sites. Furthermore, the nitrogen-doped carbon layer in the photocatalyst has a large specific surface area and good conductivity, which can promote the photoelectron migration generated by the internal transition metal clusters, while simultaneously expanding the contact area between photogenerated electrons and oxygen, thus driving... 3 O2 is reduced to ·O2 through electron transfer. － This leads to the generation of H2O2, thereby increasing the production of hydrogen peroxide.

[0022] Furthermore, the transition metal-N center of the enzyme-like material exhibits high photoreactivity. Photoexcitation can alter the local electron cloud density of the material, adjust the transition energy levels of various excited states, narrow the energy level difference between the triplet and singlet excited states, and promote [further development / reactivity]. 3 O2 is sensitized by energy transfer to 1 O2 is converted into H2O2, increasing the product concentration. After 120 min of catalytic reaction, the photocatalyst can produce 5.31 mmol·g H2O2. -1 .

[0023] Furthermore, the coordination mode of the transition metal-NC can open up new migration pathways for photogenerated carriers and improve their transport capacity, while suppressing the recombination of photogenerated electrons and holes. This adjusts the band structure of the catalyst, broadens the light absorption range, and improves the utilization rate of visible light. The photocatalyst exhibits good photostability and chemical stability.

[0024] Meanwhile, under mild conditions, the yield of juglone can reach 95.05% after the photocatalyst oxidizes 1,5-dihydroxynaphthalene for 15 min. Attached Figure Description

[0025] Figure 1 This is a TEM image of the photocatalyst (Co-NC) prepared in Example 1 of this invention;

[0026] Figure 2This is a partial TEM image of the photocatalyst (Co-NC) prepared in Example 1 of the present invention;

[0027] Figure 3 This is a mapping diagram of the photocatalyst (Co-NC) prepared in Example 1 of this invention;

[0028] Figure 4 These are the XRD patterns of the photocatalysts prepared in Examples 1-3 of this invention;

[0029] Figure 5 This is a synchrotron radiation diagram of the photocatalyst (Co-NC) prepared in Example 1 of the present invention;

[0030] Figure 6 This is a synchrotron radiation diagram (Fourier transform processing) of the photocatalyst (Co-NC) prepared in Example 1 of the present invention;

[0031] Figure 7 This is a nitrogen adsorption-desorption isotherm curve of the photocatalyst (Co-NC) prepared in Example 1 of this invention;

[0032] Figure 8 This is a pore size distribution diagram of the photocatalyst (Co-NC) prepared in Example 1 of the present invention;

[0033] Figure 9 These are the results of hydrogen peroxide production by the photocatalysts prepared in Examples 1-3 of this invention;

[0034] Figure 10 This is a graph showing the cyclic experimental results of hydrogen peroxide production by the photocatalysts prepared in Examples 1-3 of this invention;

[0035] Figure 11 This is a diagram showing the conversion of 1,5-dihydroxynaphthalene under light-protected conditions without a photocatalyst.

[0036] Figure 12 This is a diagram showing the conversion of 1,5-dihydroxynaphthalene under light conditions without a photocatalyst.

[0037] Figure 13 This is a graph showing the results of the photocatalyst (Cu-NC) prepared in Example 3 of the present invention catalyzing the conversion of 1,5-dihydroxynaphthalene under light irradiation.

[0038] Figure 14 This is a diagram showing the results of the photocatalyst (Fe-NC) prepared in Example 2 of this invention catalyzing the conversion of 1,5-dihydroxynaphthalene under light irradiation.

[0039] Figure 15 This is a diagram showing the results of the photocatalyst (Co-NC) prepared in Example 1 of this invention catalyzing the conversion of 1,5-dihydroxynaphthalene under light irradiation.

[0040] Figure 16 This is a diagram showing the results of the photocatalyst (Co″-NC) prepared in Example 5 of this invention catalyzing the conversion of 1,5-dihydroxynaphthalene under light irradiation.

[0041] Figure 17 This is a diagram showing the results of the photocatalyst (Co′-NC) prepared in Example 4 of this invention catalyzing the conversion of 1,5-dihydroxynaphthalene under light irradiation.

[0042] Figure 18 These are the results of hydrogen peroxide production by the photocatalysts prepared in Examples 1, 4 and 5 of this invention; Detailed Implementation

[0043] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0044] In this invention, unless otherwise stated, room temperature means 25±2°C.

[0045] As mentioned above, the first aspect of this invention provides a method for preparing a photocatalyst with carbon and nitrogen-coated transition metal clusters, the method comprising:

[0046] (1) In the presence of an organic solvent, a transition metal nitrate is mixed with a diaminomaleitrile, and the resulting mixture is then subjected to a hydrothermal reaction to obtain a solid product; wherein:

[0047] The transition metal nitrate is selected from at least one of cobalt nitrate, ferric nitrate, and copper nitrate;

[0048] The molar ratio of the transition metal nitrate to the diaminomaleitrile is 1:1-3;

[0049] The conditions for the hydrothermal reaction include: a hydrothermal temperature of 120-140℃ and a hydrothermal time of 8-15h.

[0050] (2) Under inert gas protection, the solid product is calcined, and then the calcined product is acid-washed; wherein:

[0051] The calcination conditions include: a heating rate of 3-10℃ / min, a calcination temperature of 450-700℃, and a calcination time of 1-4h.

[0052] According to some embodiments of the present invention, preferably, in step (1), the molar ratio of the transition metal nitrate to the diaminomaleitrile is 1:1.2-1.8. Using the above preferred embodiments, the photocatalyst obtained can achieve higher product yields in a shorter time during the catalytic production of hydrogen peroxide and the catalytic oxidation of 1,5-dihydroxynaphthalene to juglone.

[0053] According to some embodiments of the present invention, preferably, in step (1), the transition metal nitrate is cobalt nitrate. Using the above preferred embodiments, the photocatalyst obtained can achieve higher product yields (proportions) in a shorter time during the catalytic production of hydrogen peroxide and the catalytic oxidation of 1,5-dihydroxynaphthalene to juglone.

[0054] According to some embodiments of the present invention, preferably, in step (1), the organic solvent is anhydrous ethanol.

[0055] According to some embodiments of the present invention, preferably, in step (1), the amount of the organic solvent used is 70-90 mL relative to 3 mmol of the transition metal nitrate.

[0056] According to some embodiments of the present invention, preferably, in step (1), the mixing step includes: dissolving the transition metal nitrate in a first part of the organic solvent to obtain solution I; dissolving the diaminomaleitrile in a second part of the organic solvent to obtain solution II; and adding solution II dropwise to solution I at a rate of 0.4-0.8 mL / min while stirring.

[0057] Preferably, the volume ratio of the first part of the organic solvent to the second part of the organic solvent is 1:0.5-1.5.

[0058] According to some embodiments of the present invention, preferably, step (1) further includes: centrifuging the product obtained from the hydrothermal reaction, washing the centrifuged product, and finally drying the washed product to obtain the solid product. Preferably, the centrifugation conditions include: a rotation speed of 7000-9000 rpm and a time of 2-10 min. Preferably, the drying conditions include: a temperature of 40-80℃ and a time of 5-10 h.

[0059] According to some embodiments of the present invention, preferably, in step (2), the calcination conditions include: a heating rate of 4-6 °C / min, a calcination temperature of 500-600 °C, and a calcination time of 2-3 h. Using the above preferred embodiments, the photocatalyst obtained can achieve higher product yields (proportions) in a shorter time during the catalytic production of hydrogen peroxide and the catalytic oxidation of 1,5-dihydroxynaphthalene to juglone.

[0060] According to some embodiments of the present invention, preferably, in step (2), the inert gas is selected from at least one of nitrogen, argon, neon and helium.

[0061] According to some embodiments of the present invention, preferably, in step (2), the acid washing step includes: contacting the roasted product with an aqueous sulfuric acid solution under stirring conditions.

[0062] Preferably, the concentration of the sulfuric acid aqueous solution is 1-3 mol / L.

[0063] Preferably, the stirring conditions include: a stirring rate of 600-1000 rpm, a stirring temperature of 60-85℃, and a stirring time of 1-3 h.

[0064] According to some embodiments of the present invention, preferably, step (2) further includes: performing solid-liquid separation on the product obtained by acid washing, washing the solid product obtained by solid-liquid separation, and drying the washed product to obtain the photocatalyst. The method and conditions of solid-liquid separation can be performed with reference to the prior art, and there are no particular limitations thereto.

[0065] Preferably, the drying conditions include a temperature of 40-80°C and a time of 5-10 hours.

[0066] A second aspect of the present invention provides a carbon-nitrogen-coated transition metal cluster photocatalyst prepared by the method for preparing a carbon-nitrogen-coated transition metal cluster photocatalyst as described in the first aspect. The photocatalyst comprises a transition metal cluster and a nitrogen-doped carbon layer coated on the surface of the transition metal cluster. The transition metal in the transition metal cluster is selected from at least one of cobalt, iron, and copper. As measured by X-ray photoelectron spectroscopy, the mass fraction of the transition metal in the photocatalyst is 1-5%, the mass fraction of nitrogen is 15-25%, and the mass fraction of carbon is 70-80%.

[0067] According to some embodiments of the present invention, preferably, the transition metal in the transition metal cluster is cobalt. Using the above preferred embodiments, the resulting photocatalyst can achieve higher product yields in a shorter time during the catalytic production of hydrogen peroxide and the catalytic oxidation of 1,5-dihydroxynaphthalene to juglone.

[0068] According to some embodiments of the present invention, preferably, the average diameter of the transition metal cluster is 10-25 nm, and the average thickness of the nitrogen-doped carbon layer is 3-6 nm.

[0069] According to some embodiments of the present invention, preferably, the BET specific surface area of ​​the photocatalyst is 300-400 m². 2 g -1 The pore size is distributed within 3-4 nm.

[0070] A third aspect of this invention provides the application of the carbon-nitrogen-coated transition metal cluster photocatalyst described in the second aspect in the photocatalytic production of hydrogen peroxide, the application comprising:

[0071] The photocatalyst was dispersed in an aqueous sulfuric acid solution to obtain a dispersion. Air was then introduced into the dispersion and continuously bubbled. The bubbled dispersion was then subjected to a reduction reaction under light irradiation to obtain hydrogen peroxide.

[0072] According to some embodiments of the present invention, preferably, the pH value of the sulfuric acid aqueous solution is 2-4.

[0073] According to some embodiments of the present invention, preferably, the amount of the photocatalyst is 100-300 mg relative to 100 mL of the sulfuric acid aqueous solution.

[0074] According to some embodiments of the present invention, preferably, the bubbling is carried out under light-protected conditions.

[0075] According to some embodiments of the present invention, preferably, the conditions for the reduction reaction include: a temperature of 20-30°C and a time of 20-120 min, preferably 100-120 min.

[0076] According to some embodiments of the present invention, preferably, after the reduction reaction is carried out, the product obtained by the reduction reaction is filtered to obtain a filtrate containing hydrogen peroxide.

[0077] A fourth aspect of this invention provides the application of the carbon-nitrogen-coated transition metal cluster photocatalyst described in the second aspect in the photocatalytic oxidation of 1,5-dihydroxynaphthalene to juglone, the application comprising:

[0078] The dispersion containing the solvent and the photocatalyst was mixed with 1,5-dihydroxynaphthalene under stirring to obtain a mixture, which was then reacted under light to obtain juglone.

[0079] According to some embodiments of the present invention, preferably, the solvent is a combination of acetonitrile and water, wherein the volume ratio of acetonitrile to water is 1:0.5-1.5.

[0080] According to some embodiments of the present invention, preferably, the amount of the photocatalyst is 50-150 mg relative to 100 mL of the solvent.

[0081] According to some embodiments of the present invention, preferably, the amount of 1,5-dihydroxynaphthalene used is 0.5 × 10⁻⁶ mg relative to 100 mg of the photocatalyst. -4 mmol to 2×10 -4 mmol; the 1,5-dihydroxynaphthalene is provided in the form of an aqueous solution, wherein the concentration of 1,5-dihydroxynaphthalene in the aqueous solution is 0.5 × 10 mmol. -4 mol / L to 2×10 -4 mol / L.

[0082] According to some embodiments of the present invention, preferably, the mixing is carried out in the presence of oxygen and under light-protected conditions.

[0083] According to some embodiments of the present invention, preferably, the reaction conditions include: a temperature of 20-30°C and a time of 10-120 min, preferably 100-120 min.

[0084] The present invention will be described in detail below through embodiments.

[0085] In the following embodiments, unless otherwise specified, all raw materials used are commercially available products. Wherein:

[0086] Diaminomaleitrile was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., model / brand name D154866;

[0087] 1,5-Dihydroxynaphthalene was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., model / grade D109042.

[0088] In the following embodiments, the relevant parameters were measured using the following methods:

[0089] (1) Powder X-ray diffraction (PXRD) analysis

[0090] The crystal structure of the catalyst was analyzed using the X'Pert PRO MPD scanner from Panaco, Netherlands. Cu target Kα (λ = 0.15 nm) rays were used as the radiation source, with a power of 2.2 kW, tube voltage of 40 kV, tube current of 40 mA, a scanning range of 10–75°, and a scanning speed of 10° / min. -1 .

[0091] (2) Scanning electron microscopy (SEM) analysis

[0092] The apparent morphology of the catalyst was analyzed using a Hitachi SU3500 spectrometer. The operating voltage was 30 kV, and an SE probe (magnification from ×5 to ×300,000) was used, equipped with an EDS spectrometer.

[0093] (3) Transmission electron microscopy (TEM) analysis

[0094] The microstructure of the catalyst was analyzed using a JEOL JEM-2100UHR ultra-high resolution target (spot resolution up to 0.19 nm, line resolution up to 0.14 nm) and an accelerating voltage of 200 kV.

[0095] (4) X-ray photoelectron spectroscopy (XPS)

[0096] The electronic states of the catalyst surface were analyzed using a Thermo Fisher Scientific ESCALAB 250Xi X-ray source. A monochromatic Al target X-ray source and a dual-anode Al / Mg target X-ray source were employed, equipped with AES Auger electron spectroscopy, an in-situ DES main unit, and an SDD probe (sampling depth ~3 nm).

[0097] (5) Specific surface area and pore size distribution determination

[0098] The nitrogen adsorption-desorption isotherms of the catalyst were measured using a Micromeritics ASAP2020M lithography machine. Data processing was performed using the BET (Brunauer-Emmett-Teller) method.

[0099] The following examples illustrate the photocatalyst for carbon and nitrogen-coated transition metal clusters provided by the present invention and its preparation method:

[0100] Example 1

[0101] (1) In the presence of an organic solvent, 3 mmol of a transition metal nitrate was mixed with diaminomaleitrile, and the resulting mixture was then transferred to a 200 mL hydrothermal reactor for hydrothermal reaction to obtain a solid product; wherein:

[0102] The transition metal nitrate is Co(NO3)2·6H2O; the organic solvent is anhydrous ethanol;

[0103] The molar ratio of transition metal nitrate to diaminomaleonitrile is 1:1.5;

[0104] The amount of organic solvent used is 80 mL relative to 3 mmol of transition metal nitrate;

[0105] The mixing steps are as follows: a transition metal nitrate is dissolved in a first part of an organic solvent to obtain solution I; diaminomaleonitrile is dissolved in a second part of an organic solvent to obtain solution II; wherein the volume ratio of the first part of the organic solvent to the second part of the organic solvent is 1:1; under stirring, solution II is added dropwise to solution I at a rate of 0.6 mL / min using a syringe pump.

[0106] After the addition is complete, the resulting mixed solution is allowed to stand until it changes from light yellow to dark brown to obtain the above mixture;

[0107] The conditions for the hydrothermal reaction are: hydrothermal temperature of 135℃ and hydrothermal time of 12h.

[0108] After the hydrothermal reaction is completed, the product obtained from the hydrothermal reaction is centrifuged and then washed with anhydrous ethanol until the upper layer solution is colorless and transparent. Finally, the washed product is placed in an oven for drying to obtain the above solid product. The centrifugation conditions are: 8000 rpm for 5 min; the drying conditions are: 60℃ for 8 h.

[0109] (2) Under inert gas protection, the above solid product was calcined, and the calcined product (black powder) was then acid-washed to obtain a photocatalyst, denoted as Co-NC; wherein:

[0110] The inert gas is argon; the calcination conditions are: heating rate of 5℃ / min, calcination temperature of 550℃, and calcination time of 2h.

[0111] The pickling steps are as follows: under stirring conditions, the above-mentioned calcined product is added to an aqueous sulfuric acid solution for contact; the concentration of the aqueous sulfuric acid solution is 2 mol / L; the stirring conditions are: stirring speed of 700 rpm, stirring temperature of 80℃, and stirring time of 2 h.

[0112] After acid washing, the resulting solution was cooled to room temperature, and then solid-liquid separation was performed. The separated solid product was washed with anhydrous ethanol until the filtrate was neutral. The washed product was then placed in an oven for drying to obtain the above photocatalyst. The drying conditions were: temperature 60℃ and time 8h.

[0113] Example 2

[0114] The method of Example 1 is followed, except that in step (1), the transition metal nitrate is Fe(NO3)3·9H2O, and the rest are the same, to obtain a photocatalyst, denoted as Fe-NC.

[0115] Example 3

[0116] The method of Example 1 is followed, except that in step (1), the transition metal nitrate is Cu(NO3)2·3H2O, and the rest are the same, to obtain a photocatalyst, denoted as Cu-NC.

[0117] Example 4

[0118] The method is the same as in Example 1, except that:

[0119] In step (1), the molar ratio of transition metal nitrate to diaminomaleitrile is 1:3;

[0120] The conditions for the hydrothermal reaction are: hydrothermal temperature of 120℃ and hydrothermal time of 8h;

[0121] In step (2), the calcination conditions are: heating rate of 10℃ / min, calcination temperature of 650℃, and calcination time of 4h;

[0122] During the pickling process, the concentration of the sulfuric acid aqueous solution was 1 mol / L; the stirring conditions were: stirring speed of 1000 rpm, stirring temperature of 60℃, and stirring time of 1 h.

[0123] Everything else is the same, and a photocatalyst is obtained, denoted as Co′-NC.

[0124] Example 5

[0125] Following the method of Example 1, except that the calcination temperature was 700°C, all other conditions were the same, to obtain the photocatalyst Co″-NC.

[0126] The photocatalysts obtained in the above embodiments were subjected to relevant parameter measurements, including elemental content, diameter of transition metal clusters, and thickness of nitrogen-doped carbon layers. The results are shown in Table 1.

[0127] Table 1

[0128]

[0129] The present invention provides TEM images of the photocatalyst (Co-NC) prepared in Example 1, as shown in the figures below. Figure 1 and Figure 2 As shown in the figure, the center of Co-NC is a transition metal cluster composed of elemental cobalt with an average diameter of 20 nm. The surface of this cluster is covered with a nitrogen-doped carbon layer with an average thickness of 5 nm.

[0130] The mapping diagram of Co-NC obtained in Example 1 is shown below. Figure 3As shown in the figure, Co, N, and C are evenly distributed on the surface of the catalyst.

[0131] The XRD patterns of Co-NC, Fe-NC and Cu-NC prepared in Examples 1-3 are shown below. Figure 4 As shown, the XRD test results indicate that in the photocatalyst Co-NC, cobalt mainly exists in the form of elemental cobalt, and the three diffraction peaks correspond to the (100), (002) and (101) crystal planes of elemental cobalt, respectively; the diffraction pattern of Fe-NC shows a distinct broad peak, which is a characteristic of the amorphous structure; in Cu-NC, the three diffraction peaks correspond to the (001), (111) and (100) crystal planes of elemental copper, respectively.

[0132] The synchrotron radiation map of Co-NC obtained in Example 1 is shown below. Figure 5 and Figure 6 As shown in the figure, the synchrotron radiation results indicate that, compared with various standard substances, the valence state of metallic cobalt in the photocatalyst Co-NC is closer to that of elemental cobalt, further confirming the structure of the metal active center.

[0133] The nitrogen adsorption-desorption isotherm curve of Co-NC obtained in Example 1 is shown in Figure 1. Figure 7 As shown, after data processing, its BET specific surface area is 355m². 2 g -1 The pore size distribution is within 3-4 nm. Figure 8 It belongs to mesoporous materials.

[0134] Test Example 1

[0135] This test example illustrates the application of the carbon-nitrogen-coated transition metal cluster photocatalyst provided by this invention in the photocatalytic production of hydrogen peroxide.

[0136] The photocatalysts (200 mg each) prepared in the above examples were ultrasonically dispersed evenly in sulfuric acid solution (100 mL, pH = 2.5) to obtain dispersions. Then, under light-protected conditions, air was introduced into the dispersions and bubbles were continuously formed while a fan was turned on to maintain the temperature of the reaction system at room temperature. The bubbled dispersions were then subjected to a 300W xenon lamp (full spectrum, 2000 W m²). -2 Irradiation to induce a reduction reaction, at fixed intervals (see...) Figure 9 , Figure 10 and Figure 18 Samples were taken, centrifuged, and the supernatant was collected and filtered to obtain a filtrate containing hydrogen peroxide. Finally, 0.2 mol / L cerium sulfate solution was added to the filtrate, and after reacting for 3 min, the absorption spectrum of the resulting solution was measured using a UV-Vis spectrophotometer, and the absorbance at 480 nm was recorded.

[0137] A standard curve was plotted based on the concentration and absorbance of the cerium sulfate standard solution. Then, the concentrations of the cerium sulfate solution before and after the reaction were calculated. Finally, the concentration of H2O2 in the filtrate was obtained according to the stoichiometric relationship of the following reaction.

[0138] 2Ce 4+ +H₂O₂→2Ce 3+ +2H + +O2

[0139] Figure 9 , Figure 10 and Figure 18 The graph shows the results of hydrogen peroxide production from the photocatalysts prepared in Examples 1-4 and Example 5. From... Figure 9 It can be seen that in the photocatalytic production of hydrogen peroxide in the above-mentioned air-saturated acidic aqueous solution, the amount of H2O2 produced by the photocatalyst Co-NC continuously increases throughout the reaction time, reaching a maximum of 5.31 mmol·g after 120 min of reaction. -1 The catalytic effect was optimal; after 120 min of reaction with the Fe-NC photocatalyst, the yield of H2O2 was 2.76 mmol·g. -1 After 120 min of reaction with the Cu-NC photocatalyst, the yield of H2O2 was 0.59 mmol·g. -1 After three cycles of testing (the catalyst was recovered, washed with deionized water, dried, and reused), the yield of H2O2 did not show a significant decrease. Figure 10 This demonstrates that the photocatalyst provided by the present invention possesses good photostability and chemical stability, particularly the Co-NC photocatalyst. From... Figure 18 It can be seen that the amount of H2O2 produced by photocatalysis by Co′-NC and Co″-NC after 120 min was 1.85 mmol·g. -1 and 2.35 mmol·g -1 .

[0140] Test Example 2

[0141] This test example illustrates the application of the carbon-nitrogen-coated transition metal cluster photocatalyst provided by the present invention in the photocatalytic oxidation of 1,5-dihydroxynaphthalene to produce juglone.

[0142] The photocatalysts (100 mg each) prepared in the above examples were uniformly dispersed in a mixed solution of acetonitrile and water (100 mL, volume ratio of acetonitrile to water 1:1) to obtain a dispersion. Then, 1 mL of a 1,5-dihydroxynaphthalene aqueous solution (concentration 1×10⁻⁶) was added to the dispersion. -4The mixture (mol / L) was stirred for 30 min at room temperature, in air, and in the dark to allow the reactants to reach adsorption-desorption equilibrium on the catalyst surface, resulting in a mixture. This mixture was then subjected to a 120 W / m... 2 The reaction is initiated by illuminating white LED lights at fixed intervals (see...). Figure 11-17 Sampling was performed, and after centrifugation, the supernatant was collected, filtered, and the absorption spectrum of the filtrate was measured using a UV-Vis spectrophotometer. 1,5-DHN showed three absorption peaks in the 300-330 nm range, while the product juglone showed one absorption peak at 425±3 nm. The yield Y1 of juglone was then calculated using the following formula:

[0143] Y1 = 100% × (I1 ÷ ε1 ÷ L) ÷ C1

[0144] Where I1 is the absorbance of juglone, and ε1 is the molar extinction coefficient of juglone (3567 L·mol⁻¹). -1 ·cm -1 L is the thickness of the filtrate measured (1 cm), and C1 is the initial concentration of 1,5-DHN.

[0145] Figure 11-17 The figures show the results of the photocatalysts prepared in Examples 1-4 and Example 5 for the conversion of 1,5-dihydroxynaphthalene. As can be seen from the figures, in the above-mentioned photocatalytic oxidation of 1,5-dihydroxynaphthalene to juglone, no juglone product was detected under conditions without a photocatalyst, regardless of whether there was light irradiation (see Figure 5). Figure 11 and 12 This indicates that 1,5-DHN was not converted and that light irradiation itself could not drive the oxidation of 1,5-DHN. Under light irradiation and Cu-NC catalysis, the yield of juglone was 41.49% after 60 min of reaction (see...). Figure 13 ); Under Fe-NC catalysis, the yield of juglone was 77.10% after 120 min of reaction. Figure 14 ); Under Co-NC catalysis, the yield of juglone reached 95.05% after only 15 minutes of reaction. Figure 15 ); When catalyzed by Co′-NC and Co″-NC, the yields of juglone were 34.27% after 80 min of reaction. Figure 16 ) and 40.58% Figure 17 ).

[0146] The results above show that the photocatalyst for carbon-nitrogen-coated transition metal clusters provided by this invention has good photostability and chemical stability, and can improve the yield of hydrogen peroxide and the yield of juglone.

[0147] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. The application of a carbon-nitrogen-coated transition metal cluster photocatalyst in the photocatalytic production of hydrogen peroxide, the application comprising: The photocatalyst was dispersed in an aqueous sulfuric acid solution to obtain a dispersion. Air was then introduced into the dispersion and continuously bubbled. The bubbled dispersion was then subjected to a reduction reaction under light irradiation to obtain hydrogen peroxide. The photocatalyst comprises a transition metal cluster and a nitrogen-doped carbon layer coating the surface of the transition metal cluster; the transition metal in the transition metal cluster is selected from at least one of cobalt, iron, and copper; and the mass fraction of the transition metal in the photocatalyst, as measured by X-ray photoelectron spectroscopy, is 1-5%, the mass fraction of nitrogen is 15-25%, and the mass fraction of carbon is 70-80%. The photocatalyst with carbon and nitrogen-coated transition metal clusters was prepared by the following method: (1) In the presence of an organic solvent, a transition metal nitrate is mixed with a diaminomaleitrile, and the resulting mixture is then subjected to a hydrothermal reaction to obtain a solid product; wherein: The transition metal nitrate is selected from at least one of cobalt nitrate, ferric nitrate, and copper nitrate; The molar ratio of the transition metal nitrate to the diaminomaleitrile is 1:1-3; The conditions for the hydrothermal reaction include: a hydrothermal temperature of 120-140℃ and a hydrothermal time of 8-15h. (2) Under inert gas protection, the solid product is calcined, and then the calcined product is acid-washed; wherein: The calcination conditions include: a heating rate of 3-10℃ / min, a calcination temperature of 450-700℃, and a calcination time of 1-4h.

2. The application according to claim 1, wherein, The pH value of the sulfuric acid aqueous solution is 2-4.

3. The application according to claim 1, wherein, The amount of photocatalyst used is 100-300 mg relative to 100 mL of the sulfuric acid aqueous solution.

4. The application according to claim 1, wherein, The bubbling is carried out under light-protected conditions; the conditions for the reduction reaction include a temperature of 20-30℃ and a time of 20-120 min.

5. The application according to claim 4, wherein, The bubbling is carried out under light-protected conditions; the conditions for the reduction reaction include: a temperature of 20-30℃ and a time of 100-120 min.

6. The application according to any one of claims 1-5, wherein, The average diameter of the transition metal clusters is 10-25 nm, and the average thickness of the nitrogen-doped carbon layer is 3-6 nm.

7. The application according to any one of claims 1-5, wherein, The photocatalyst has a BET specific surface area of ​​300-400 m². 2 g -1 The pore size is distributed within 3-4 nm.

8. The application according to any one of claims 1-5, wherein, In step (1), the molar ratio of the transition metal nitrate to the diaminomaleitrile is 1:1.2-1.

8.

9. The application according to any one of claims 1-5, wherein, In step (1), the transition metal nitrate is cobalt nitrate.

10. The application according to any one of claims 1-5, wherein, In step (1), the organic solvent is anhydrous ethanol; the amount of the organic solvent used is 70-90 mL relative to 3 mmol of the transition metal nitrate.

11. The application according to any one of claims 1-5, wherein, In step (1), the mixing step includes: dissolving the transition metal nitrate in a first part of the organic solvent to obtain solution I; dissolving the diaminomaleitrile in a second part of the organic solvent to obtain solution II; wherein the volume ratio of the first part of the organic solvent to the second part of the organic solvent is 1:0.5-1.5; and adding solution II dropwise to solution I at a rate of 0.4-0.8 mL / min while stirring.

12. The application according to any one of claims 1-5, wherein, In step (2), the calcination conditions include: a heating rate of 4-6℃ / min, a calcination temperature of 500-600℃, and a calcination time of 2-3h.

13. The application according to any one of claims 1-5, wherein, In step (2), the inert gas is selected from at least one of nitrogen, argon, neon and helium.

14. The application according to any one of claims 1-5, wherein, In step (2), the acid washing step includes: contacting the roasted product with an aqueous sulfuric acid solution under stirring conditions.

15. The application according to claim 14, wherein, The concentration of the sulfuric acid aqueous solution is 1-3 mol / L.

16. The application according to claim 14, wherein, The stirring conditions include: a stirring speed of 600-1000 rpm, a stirring temperature of 60-85℃, and a stirring time of 1-3 hours.

17. The application of a carbon-nitrogen-coated transition metal cluster photocatalyst in the photocatalytic oxidation of 1,5-dihydroxynaphthalene to juglone, the application comprising: The dispersion containing the solvent and the photocatalyst was mixed with 1,5-dihydroxynaphthalene under stirring to obtain a mixture, and then the mixture was reacted under light to obtain juglone. The solvent is a combination of acetonitrile and water, wherein the volume ratio of acetonitrile to water is 1:0.5-1.5; the amount of photocatalyst used is 50-150 mg relative to 100 mL of the solvent; the amount of 1,5-dihydroxynaphthalene used is 0.5 × 10⁻⁶ mg relative to 100 mg of the photocatalyst. -4 mmol to 2×10 -4 mmol; The photocatalyst comprises a transition metal cluster and a nitrogen-doped carbon layer coating the surface of the transition metal cluster; the transition metal in the transition metal cluster is selected from at least one of cobalt, iron, and copper; and the mass fraction of the transition metal in the photocatalyst, as measured by X-ray photoelectron spectroscopy, is 1-5%, the mass fraction of nitrogen is 15-25%, and the mass fraction of carbon is 70-80%. The photocatalyst with carbon and nitrogen-coated transition metal clusters was prepared by the following method: (1) In the presence of an organic solvent, a transition metal nitrate is mixed with a diaminomaleitrile, and the resulting mixture is then subjected to a hydrothermal reaction to obtain a solid product; wherein: The transition metal nitrate is selected from at least one of cobalt nitrate, ferric nitrate, and copper nitrate; The molar ratio of the transition metal nitrate to the diaminomaleitrile is 1:1-3; The conditions for the hydrothermal reaction include: a hydrothermal temperature of 120-140℃ and a hydrothermal time of 8-15h. (2) Under inert gas protection, the solid product is calcined, and then the calcined product is acid-washed; wherein: The calcination conditions include: a heating rate of 3-10℃ / min, a calcination temperature of 450-700℃, and a calcination time of 1-4h.

18. The application according to claim 17, wherein, The 1,5-dihydroxynaphthalene is provided in the form of an aqueous solution, wherein the concentration of 1,5-dihydroxynaphthalene in the aqueous solution is 0.5 × 10⁻⁶. -4 mol / L to 2×10 -4 mol / L.

19. The application according to claim 17, wherein, The mixing is carried out in the presence of oxygen and under light-protected conditions; the reaction conditions include a temperature of 20-30°C and a time of 10-120 min.

20. The application according to claim 19, wherein, The mixing is carried out in the presence of oxygen and under light-protected conditions; the reaction conditions include a temperature of 20-30°C and a time of 100-120 min.

21. The application according to any one of claims 17-20, wherein, The average diameter of the transition metal clusters is 10-25 nm, and the average thickness of the nitrogen-doped carbon layer is 3-6 nm.

22. The application according to any one of claims 17-20, wherein, The photocatalyst has a BET specific surface area of ​​300-400 m². 2 g -1 The pore size is distributed within 3-4 nm.

23. The application according to any one of claims 17-20, wherein, In step (1), the molar ratio of the transition metal nitrate to the diaminomaleitrile is 1:1.2-1.

8.

24. The application according to any one of claims 17-20, wherein, In step (1), the transition metal nitrate is cobalt nitrate.

25. The application according to any one of claims 17-20, wherein, In step (1), the organic solvent is anhydrous ethanol; the amount of the organic solvent used is 70-90 mL relative to 3 mmol of the transition metal nitrate.

26. The application according to any one of claims 17-20, wherein, In step (1), the mixing step includes: dissolving the transition metal nitrate in a first part of the organic solvent to obtain solution I; dissolving the diaminomaleitrile in a second part of the organic solvent to obtain solution II; wherein the volume ratio of the first part of the organic solvent to the second part of the organic solvent is 1:0.5-1.5; and adding solution II dropwise to solution I at a rate of 0.4-0.8 mL / min while stirring.

27. The application according to any one of claims 17-20, wherein, In step (2), the calcination conditions include: a heating rate of 4-6℃ / min, a calcination temperature of 500-600℃, and a calcination time of 2-3h.

28. The application according to any one of claims 17-20, wherein, In step (2), the inert gas is selected from at least one of nitrogen, argon, neon and helium.

29. The application according to any one of claims 17-20, wherein, In step (2), the acid washing step includes: contacting the roasted product with an aqueous sulfuric acid solution under stirring conditions.

30. The application according to claim 29, wherein, The concentration of the sulfuric acid aqueous solution is 1-3 mol / L.

31. The application according to claim 29, wherein, The stirring conditions include: a stirring speed of 600-1000 rpm, a stirring temperature of 60-85℃, and a stirring time of 1-3 hours.

Images