Sulfonic acid group functionalized c3n4 catalysts and their application in photocatalytic synthesis of epoxidized methyl oleate

Abstract

The application discloses a sulfonic acid group functionalized C3N4 catalyst and application thereof in synthesis of photocatalytic epoxy methyl oleate, and relates to a method for synthesizing epoxy methyl oleate by one-step epoxidation of methyl oleate under visible light irradiation at room temperature, normal pressure and neutral reaction conditions, with the sulfonic acid group functionalized C3N4 as a heterogeneous visible light catalyst and air as an O2 source. The synthesis method has the characteristics of atom economy of a synthesis route, direct use of air as an O2 source, no need of additional hydrogen peroxide, high activity of a catalytic system, good selectivity, recyclability and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical products and its preparation technology, and particularly relates to synthesis of a series of sulfonic acid functionalized C3N4; a method for synthesizing methyl epoxy oleate by one-step epoxidation of methyl oleate under visible light irradiation at room temperature, normal pressure and neutral reaction conditions, with the synthesized sulfonic acid functionalized C3N4 as a heterogeneous visible light catalyst and air as an O2 source. BACKGROUND

[0002] Epoxy methyl oleate (EMO) is a new generation of non-toxic, environmentally friendly and environmentally friendly plasticizer, which is an ideal substitute for phthalate plasticizers. EMO has excellent biocompatibility, renewability, water resistance, oil resistance and weather resistance. It can also be used as a good PVC stabilizer. The active three-membered oxygen ring structure of EMO can effectively prevent the continuous degradation of PVC by ring-opening addition with hydrogen chloride generated during the thermal decomposition of PVC, which can significantly improve the stability of plastic products. In 2016, China's total plasticizer production capacity was 7.5 million tons, of which the production capacity of phthalate plasticizers was about 2.73 million tons, accounting for one-third of the total production capacity. The EMO consumer market has great potential. In recent years, with the popularization of biodiesel in China, methyl oleate has a sufficient and cheap source, which lays the foundation for large-scale industrial synthesis and application of EMO based on methyl oleate. The current EMO synthesis process is divided into homogeneous and heterogeneous two categories, among which the homogeneous process is most representative with Rrilezhaev epoxidation [A. Campanella, C. Fontanini, et al. High yield epoxidation of fatty acid methylesters with performic acid generated in-situ [J]. Chem. Eng. J. 2008, 144: 466-475.]. This process uses inorganic liquid strong acid (such as sulfuric acid, hydrochloric acid, phosphoric acid, etc.) as catalyst, industrial hydrogen peroxide as oxidant, and excessive formic acid or acetic acid to generate in-situ peroxymethanoic acid or peroxoacetic acid. Both of them are active oxidation intermediates that epoxidize the double bond in the molecular structure of oleic acid. This method avoids the shortcomings of directly using organic peroxy acid, but the catalytic system has low activity, poor selectivity, many side reactions, difficult separation, equipment corrosion, large amount of three wastes, dark color, low epoxy value, and production safety hazards (the reaction process is strong exothermic). Developing a direct oxidation method with molecular oxygen and hydrogen peroxide as green oxidants has become a research hotspot. Enzymatic epoxidation [X. Zhang, J. Liu, et al. Enzymatic epoxidation of high oleic soybean oil [J]. ACS Sustain. Chem. Eng., 2018, 6: 8578-8583.] has the advantages of mild reaction conditions, direct use of molecular oxygen as oxidant, and high selectivity, but there are problems such as domestication, directed evolution, and compatibility with organic solvents. Currently, there is no industrial application.In 1997, Corma et al. [A. Camblor, M. Corma, et al. Epoxidation of unsaturated fatty esters over large pore Ti-containing molecular sieves as catalysts: important role of the hydrophobic-hydrophilic properties of the molecular sieve [J]. Chem. Commun., 1997, 759-765.] introduced titanium into microporous β zeolite and mesoporous molecular sieve structure, activated H2O2 and TBHP with Ti's mild Lewis acidity, in which Ti-β zeolite showed good catalytic activity. On the basis of this report, Lin et al. [Y. Zhang, M. Lin, et al. Sponge-sturctured titanosilicate zeolite with high catalytic activity in epoxidation of fatty methyl ester [J]. 2017, Catal. Commun., 101: 1-4] synthesized sponge-structured titanosilicate zeolite TS-1 by post-hydrothermal treatment method, under solvent-free reaction conditions, TBHP as an oil-soluble oxidant, 90℃ for 3 hours, the conversion rate of methyl oleate was as high as 99%. The shortcomings of the above solid-phase synthesis are uneven distribution of active sites in the catalytic system, the need for high concentration of hydrogen peroxide in the reaction, and limited mass and heat transfer. In view of the characteristics of the reaction between hydrogen peroxide and methyl oleate as a two-phase reaction, Feng et al. [Feng Shu-Bo, Yang Hua, et al. Quaternary ammonium phosphotungstate catalyzed epoxidation of fatty acid methyl ester [J]. Molecular Catalysis, 2010, 24(3): 222-227] designed the molecular structure of heteropoly acid, and constructed a heteropoly acid-based ionic hybrid with both oxidation and phase transfer catalytic activity by self-assembly of long-chain quaternary ammonium cations as counter cations and phosphotungstate anions. The epoxy value of the catalytic product EMO reached 5.7, and the results showed that the introduction of amphiphilic activity was an effective strategy to promote the design of the catalytic system for the epoxidation of methyl oleate. The reported shortcomings are that the catalyst is not heat stable in the reaction system, the active site is easy to lose, and it is difficult to separate and recycle. Hydrogen peroxide as a green oxidant has the advantages of high active oxygen content, only water as the byproduct, and direct use in liquid phase. However, as a representative of high energy consumption, high pollution, and high use risk industrial chemicals, it limits its large-scale application in the industrial synthesis of EMO.

[0003] The application directly starts from molecular oxygen, and performs molecular modification and redesign on the organic semiconductor g-C3N4 at a molecular level, introduces sulfonic acid group functional groups while maintaining good photocatalytic activity, introduces strong hydrophilic units on the hydrophobic surface while maintaining the acidity, and obtains functionalized g-C3N4 with an amphiphilic surface The application utilizes the photon electrons generated by the functionalized g-C3N4 under visible light excitation to reduce molecular oxygen and water to generate hydrogen peroxide, and in-situ oxidizes the sulfonic acid group functional groups to peroxymonosulfate, which is a high-activity oxidation intermediate, and one-step epoxidizes methyl oleate to EMO, and realizes the low-carbon and high-efficiency green synthesis of EMO driven by visible light under room temperature, normal pressure and neutral reaction conditions, with molecular oxygen as an oxidant. SUMMARY

[0004] One of the purposes of the application is to introduce sulfonic acid group functional groups on the N atoms of the primary amine group functional groups in the C3N4 structure through thermal polycondensation reaction of dicyandiamide (S), melamine (M), cyanuric acid melamine (MCR) as C3N4 synthesis precursors and ammonium persulfate or potassium hydrogen persulfate or tetrabutylammonium persulfate as sulfonic acid group precursor compounds, in a covalent bond way (sulfonylation), to obtain a kind of functionalized C3N4 with photocatalytic activity, acid catalytic activity, and a nanosheet stacking morphology. The size of the photocatalytic activity and the acid catalytic activity is adjusted by the type and number of the synthesis precursor compounds; the sulfonic acid group functional groups in the C3N4 molecular structure The acid catalytic site and the photocatalytic site are spatially separated, the generated hydrogen peroxide is oxidized in-situ to peroxymonosulfate, and the two-step photo / chemical reaction of the photocatalytic oxidation to generate hydrogen peroxide and the in-situ oxidation of the sulfonic acid group functional groups to peroxymonosulfate is realized; the sulfonic acid group functional groups in the C3N4 structure are microporous to macroporous, and the inner cavity is a micropore with amphiphilic properties, which provides a good microenvironment for the smooth reaction of hydrogen peroxide and methyl oleate in two phases.

[0005] To achieve the above purposes, the application adopts the following technical solutions:

[0006] A sulfonic acid group functionalized g-C3N4 catalyst, the sulfonic acid group functional groups are introduced into the N atoms of the active amino groups in the g-C3N4 molecular structure in a covalent bond form, the introduction of the sulfonic acid group makes the functionalized g-C3N4 have photocatalytic oxidation activity, acidity and good surface amphiphilic activity, and the catalytic sites are spatially separated; the three activities can be controlled by the type and amount of the synthesis precursors; the functionalized g-C3N4 presents a nanosheet layer stacking morphology, and the layer distribution size is microporous to macroporous, and the inner cavity is a pore with amphiphilic properties.

[0007] The sulfonic acid group functionalized g-C3N4 is synthesized by thermal polycondensation reaction under nitrogen atmosphere, using dicyandiamide (S) or melamine (M) or melamine cyanurate (MCR), ammonium persulfate (1) or potassium persulfate (2) or tetrabutylammonium persulfate (3) as starting materials, and ammonium chloride (a) or ammonium oxalate (b) as a gas-phase template. a-b -3 a-b , SO3H-[C3N4]-M-1 a-b -3 a-b , SO3H-[C3N4]-MCR-1 a-b -3 a-b The schematic structure of the sulfonic acid group functionalized C3N4 is shown in Figure 1

[0008] Further, the synthesis of the sulfonic acid group functionalized g-C3N4 includes the following steps: after the dicyandiamide or melamine or melamine cyanurate is sufficiently mixed and ground with different amounts of ammonium persulfate or ammonium persulfate or tetrabutylammonium persulfate and a gas-phase template (ammonium chloride or ammonium oxalate), it is placed in a gas atmosphere box furnace, nitrogen is continuously introduced (5-15 ml / min), the heating rate is controlled at 1.2-2.5 ℃ / min, heated to 500-620 ℃, and reacted for 3-5 h. The crude product is sufficiently ground, washed with deionized water and ethanol, and vacuum dried to constant weight to obtain the target product.

[0009] The second object of the present application is to provide a method for synthesizing EMO by one-step photocatalytic epoxidation of methyl oleate using the above sulfonic acid group functionalized g-C3N4 as a heterogeneous visible light catalyst, directly using air as the O2 source, under room temperature, normal pressure and neutral reaction conditions, and under visible light irradiation. This synthesis method has the characteristics of atom economy in the synthesis route, directly using air as the O2 source, without the need for additional hydrogen peroxide, high activity of the catalytic system, good selectivity, recyclability, etc.

[0010] To solve the above technical problems, the technical solution provided by the present application is:

[0011] A method for synthesizing EMO by one-step photocatalytic epoxidation of methyl oleate using the above sulfonic acid group functionalized g-C3N4 as a visible light catalyst, air as the O2 source, under room temperature, normal pressure and neutral reaction conditions, and under visible light irradiation, includes the following steps:

[0012] ​S300: In a quartz photochemical reaction flask equipped with magnetic stirring and circulating cooling water, 10 mg of sulfonic acid functionalized g-C3N4, 20 ml of ion-free water, and 3 ml of ethanol were sequentially added. The stirring was turned on, and the mixture was irradiated under a 300 W xenon lamp (with a 420 nm filter) or an LED lamp (60 W) while continuously bubbling air. The reaction was carried out for 2-4 h. Then, 12 ml of methyl oleate was added, and the reaction was continued under light irradiation and continuous air bubbling for 4-6 h. The phases were separated by standing, and the catalyst was separated by centrifugation. The organic phase was dried with anhydrous magnesium sulfate and filtered to obtain the target product. The yield was 74.6-93.2%, the iodine value was 2.5-3.1 (g I2 / 100 g), the epoxy value was 3.2-4.5 (g / 10 g), and the color number was (Pt-Co) <150, reaching the EMO first-class product index.

[0013] The regeneration and recycling of sulfonic acid functionalized g-C3N4: The sulfonic acid functionalized g-C3N4 separated by centrifugation in step S300 was washed with ethanol, diethyl ether, and ion-free water, and then dried at 60°C under vacuum until the weight was constant. This completed the regeneration of sulfonic acid functionalized g-C3N4. The regenerated g-C3N4 was used in the same way as in S300, except that the newly prepared g-C3N4 was replaced by the regenerated g-C3N4.

[0014] The present application uses dicyandiamide or melamine or melamine cyanurate as the C3N4 synthesis precursor, ammonium persulfate or potassium persulfate or tetrabutylammonium persulfate as the sulfonic acid functional group introduction precursor, and ammonium chloride or ammonium oxalate as the gas phase template agent. Under a nitrogen atmosphere, 18 kinds of sulfonic acid functionalized g-C3N4 are constructed through thermal polycondensation reaction, and the target compounds have photocatalytic activity, acidic activity, and the two catalytic sites are spatially separated; the two catalytic activities can be controlled by the types and amounts of g-C3N4 precursors and sulfonic acid precursors. This series of sulfonic acid functionalized g-C3N4 is a synthetic compound that does not exist in nature. It is obtained through scientific and careful theoretical design and repeated exploration of different reaction conditions in the laboratory.

[0015] The above synthesized sulfonic acid functionalized g-C3N4 is used as a heterogeneous visible light catalyst, and air is used as the O2 source. Under room temperature, normal pressure, and neutral reaction conditions, methyl oleate is synthesized into EMO through one-step photocatalytic epoxidation under visible light irradiation. The sulfonic acid functionalized g-C3N4 can be regenerated and recycled after centrifugation, washing, and vacuum drying. The yield of EMO remains basically unchanged after 3 cycles of recycling.

[0016] The beneficial effects of the present application are:

[0017] 1. In the sulfonic acid group functionalized g-C3N4 structure, the sulfonic acid group is covalently combined with the N atom of the active primary amino group in the g-C3N4 structure, and the target compound has photocatalytic activity, acid activity, and the two catalytic sites are spatially separated from each other, so that the photocatalytic reaction of generating hydrogen peroxide by photocatalytic molecular oxygen reduction and the chemical oxidation reaction of generating peroxymonosulfonic acid in situ can be carried out in a two-step process.

[0018] 2. The target compound presents a nanosheet layer accumulation morphology, the nanosheet thickness is about 10 nm, and the surface is distributed with relatively uniform protrusions, and the microporous channels with amphiphilic active lumen of 20-300 nm are formed by interlayer accumulation.

[0019] 3. The sulfonic acid group functionalized g-C3N4 is used as a heterogeneous visible light catalyst, air is used as the O2 source, and methyl oleate is synthesized by one-step photocatalytic epoxidation under room temperature, normal pressure and neutral reaction conditions.

[0020] 3. The sulfonic acid group functionalized g-C3N4 is centrifuged, washed with diethyl ether and ion-free water, and vacuum dried to constant weight, and can be regenerated and recycled, and the catalytic activity basically remains unchanged after 5 cycles. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure shows the synthesis route and structure of the sulfonic acid group functionalized g-C3N4 described in the application;

[0022] Figure 2 The figure shows the synthesis route of methyl oleate catalyzed by the sulfonic acid group functionalized g-C3N4 described in the application;

[0023] Figure 3 The scanning electron microscope (SEM) image of the sulfonic acid group functionalized g-C3N4 (SO3H-C3N4-MCR-3b) described in the application. DETAILED DESCRIPTION

[0024] The application will be further described below in combination with specific embodiments, but the application is not limited to only these embodiments.

[0025] Example 1: SO3H-[C3N4]-S-1 a , SO3H-[C3N4]-M-1 a , SO3H-[C3N4]-MCR-1 a Synthesis of

[0026] Step S101: 3 g of dicyandiamide, 0.6 g of ammonium persulfate and 1 g of ammonium chloride were sequentially added into a mortar, and mixed and ground thoroughly. The mixture was placed in an atmosphere muffle furnace, nitrogen was continuously introduced at 5 ml / min, the temperature was controlled to increase at a rate of 2.0 ℃ / min, and heated to 550 ℃ for 4 h, and then naturally cooled to room temperature. The crude product was thoroughly ground, washed with deionized water and ethanol, and vacuum dried to constant weight to obtain the target product SO3H-[C3N4]-S-1. a .

[0027] FT-IR (KBr), v / cm-1: 3434, 3078, 1626, 1532, 1450, 1386, 1307. －1 .

[0028] XRD: 12, 27

[0029] Step S102: Except that 3 g of melamine was replaced by dicyandiamide, other operations were the same as S101, to obtain the target product SO3H-[C3N4]-M-1. a

[0030] FT-IR (KBr), v / cm-1: 3417, 3137, 2932, 1630, 1573, 1542, 1456, 1404, 1300, 1270. －1 .

[0031] XRD: 13, 28

[0032] Step S103: Except that 4 g of cyanuric acid melamine was replaced by dicyandiamide, other operations were the same as S101, to obtain the target product SO3H-[C3N4]-MCR-1. a

[0033] FT-IR (KBr), v / cm-1: 3425, 3035, 2920, 1634, 1581, 1537, 1450, 1394, 1295, 1270. －1 .

[0034] XRD: 8, 11, 28

[0035] Example 2: Synthesis of SO3H-[C3N4]-S-1, b , SO3H-[C3N4]-M-1, b , SO3H-[C3N4]-MCR-1 b .

[0036] Step S201: Except that 1 g of ammonium oxalate was replaced by ammonium chloride, other operations were the same as S101, to obtain the target product SO3H-[C3N4]-S-1. b

[0037] FT-IR (KBr), v / cm-1 －1 : 3432, 3076, 1628, 1530, 1452, 1387, 1308.

[0038] XRD: 12, 27

[0039] Step S202: Replace 3g melamine with dicyandiamide, and other operations are the same as S201, to obtain the target product SO3H-[C3N4]-M-1 b

[0040] FT-IR (KBr), v / cm-1 －1 : 3419, 3126, 2930, 1633, 1570, 1539, 1452, 1400, 1304, 1276.

[0041] XRD: 13, 28

[0042] Step S203: Replace 4g cyanuric acid with dicyandiamide, and other operations are the same as S201, to obtain the target product SO3H-[C3N4]-MCR-1 b

[0043] FT-IR (KBr), v / cm-1 －1 : 3417, 3040, 2925, 1629, 1584, 1530, 1453, 1389, 1293, 1275.

[0044] XRD: 8, 11, 28

[0045] Example 3: SO3H-[C3N4]-S-3 b , SO3H-[C3N4]-M-3 b , SO3H-[C3N4]-MCR-3 b

[0046] Step S301: Add 3g dicyandiamide, 0.7g tetrabutylammonium persulfate, and 1g ammonium oxalate in a mortar in turn, mix and grind thoroughly. Place the mixture in an atmospheric muffle furnace, continuously introduce nitrogen at 5ml / min, control the heating rate at 2.0℃ / min, heat to 550℃ and keep for 4h, and naturally cool to room temperature. The crude product is washed with ion-free water and ethanol thoroughly, and dried in vacuum to constant weight, to obtain the target product SO3H-[C3N4]-S-3 b .

[0047] FT-IR (KBr), v / cm-1 －1 ​: 3425, 3068, 1630, 1525, 1452, 1389, 1302.

[0048] XRD: 27, 41, 50, 59, 65

[0049] Step S302: Except that 3g melamine is replaced by dicyandiamide, other operations are the same as S301, to obtain the target product SO3H-[C3N4]-M-3 b

[0050] FT-IR (KBr), v / cm-1 －1 : 3383, 3100, 1621, 1522, 1443, 1377, 1296.

[0051] XRD: 26, 41, 52, 60, 66

[0052] Step S303: Except that 4g cyanuric acid is replaced by dicyandiamide, and the amount of tetrabutylammonium persulfate is 0.9g, other operations are the same as S301, to obtain the target product SO3H-[C3N4]-MCR-3 b

[0053] FT-IR (KBr), v / cm-1 －1 : 3340, 3090, 1618, 1530, 1439, 1371, 1289.

[0054] XRD: 14, 27, 40, 51, 60, 65

[0055] Example 4: SO3H-[C3N4]-S-3 a , SO3H-[C3N4]-M-3 a , SO3H-[C3N4]-MCR-3 a

[0056] Step S401: 3g dicyandiamide, 0.7g tetrabutylammonium persulfate, and 1g ammonium chloride are sequentially added in a mortar, and mixed and ground thoroughly. The mixture is placed in an atmospheric muffle furnace, the heating rate is controlled at 2.0℃ / min, heated to 550℃ and kept for 4h, and naturally cooled to room temperature. The crude product is thoroughly ground, washed with deionized water and ethanol, and vacuum dried to constant weight, to obtain the target product SO3H-[C3N4]-S-3 a .

[0057] FT-IR (KBr), v / cm-1 －1 : 3423, 3056, 1632, 1528, 1449, 1381, 1305.

[0058] XRD: 27, 40, 50, 58, 65​

[0059] Step S402: replace 3g melamine with dicyandiamide, other operations are the same as S401, to obtain the target product SO3H-[C3N4]-M-3 a

[0060] FT-IR (KBr), v / cm-1: 3368, 3006, 1625, 1520, 1439, 1368, 1293. －1

[0061] XRD: 26, 41, 51, 60, 65

[0062] Step S403: replace 4g cyanuric acid with dicyandiamide, other operations are the same as S401, to obtain the target product SO3H-[C3N4]-MCR-3 a

[0063] FT-IR (KBr), v / cm-1: 3361, 3080, 1622, 1536, 1427, 1375, 1279. －1

[0064] XRD: 13, 27, 41, 50, 60, 65

[0065] Example 5: Synthesis of SO3H-[C3N4]-S-2 a , SO3H-[C3N4]-M-2 a , SO3H-[C3N4]-MCR-2 a

[0066] Step S501: add 3g dicyandiamide, 0.7g potassium persulfate, and 1g ammonium chloride in a mortar in turn, mix and grind thoroughly. Put the mixture in an atmosphere muffle furnace, continuously introduce nitrogen at 5ml / min, control the heating rate at 2.0℃ / min, heat to 550℃ and keep for 4h, and naturally cool to room temperature. The crude product is washed with ion-free water and ethanol thoroughly, and dried in vacuum to constant weight, to obtain the target product SO3H-[C3N4]-S-2 a .

[0067] FT-IR (KBr), v / cm-1: 3428, 3056, 1622, 1528, 1445, 1382, 1297. －1

[0068] XRD: 12, 27

[0069] Step S502: replace 3g melamine with dicyandiamide, other operations are the same as S501, to obtain the target product SO3H-[C3N4]-M-2 a ​​​​

[0070] FT-IR (KBr), v / cm －1 : 3422, 3115, 2927, 1631, 1568, 1448, 1395, 1303, 1275.

[0071] XRD: 13, 27

[0072] Step S503: Replace 4 g melamine cyanuric acid complex with dicyandiamide, and other operations S501 to obtain the target product SO3H-[C3N4]-MCR-2 a

[0073] FT-IR (KBr), v / cm －1 : 3431, 3028, 2932, 1630, 1577, 1532, 1447, 1396, 1291, 1266.

[0074] XRD: 8, 11, 27

[0075] Example 6: SO3H-[C3N4]-S-2 b , SO3H-[C3N4]-M-2 b , SO3H-[C3N4]-MCR-2 b

[0076] Step S601: Add 3 g dicyandiamide, 0.7 g potassium persulfate, and 1 g ammonium oxalate in a mortar in sequence, mix and grind thoroughly. Place the mixture in an atmospheric muffle furnace, continuously introduce nitrogen at 5 ml / min, control the heating rate at 2.0 ℃ / min, heat to 550 ℃ and keep for 4 h, and naturally cool to room temperature. The crude product is washed with ion-free water and ethanol thoroughly, and vacuum dried to constant weight to obtain the target product SO3H-[C3N4]-S-2 b .

[0077] FT-IR (KBr), v / cm －1 : 3425, 3068, 1630, 1525, 1452, 1389, 1302.

[0078] XRD: 12, 27

[0079] Step S602: Replace 3 g melamine with dicyandiamide, and other operations are the same as S601 to obtain the target product SO3H-[C3N4]-M-2 b

[0080] FT-IR (KBr), v / cm －1 : 3341, 3053, 1620, 1527, 1439, 1381, 1294. ​

[0081] XRD: 13, 27

[0082] Step S603 replaces melamine cyanuric acid with dicyandiamide, and other operations are the same as S601, to obtain the target product SO3H-[C3N4]-MCR-2 b

[0083] FT-IR (KBr), v / cm －1 : 3329, 3077, 1618, 1530, 1439, 1366, 1284.

[0084] XRD: 8, 13, 27

[0085] Example 1: Synthesis of methyl oleate by photocatalytic epoxidation of methyl oleate

[0086] In a quartz photo-reactor flask equipped with magnetic stirring and circulating cooling water, 10 mg of sulfonic acid functionalized g-C3N4, 20 ml of ion-free water, and 3 ml of ethanol were sequentially added. Stirring was started, and the mixture was irradiated under a 300 W xenon lamp light source (with a 420 nm filter) or an LED lamp (60 W) while continuously bubbling air. The reaction was carried out for 2-4 h. Then, 12 ml of methyl oleate was added, and the reaction was continued under irradiation and continuous air bubbling for 4-6 h. After phase separation, the catalyst was separated by centrifugation. The organic phase was dried with anhydrous magnesium sulfate and filtered to obtain the target product, with a yield of 74.6-93.2%.

[0087] Table 1: Results of sulfonic acid functionalized C3N4 photocatalytic epoxidation of methyl oleate

[0088]

[0089] [1] Catalyst was added and reacted for 4 h; methyl oleate was added and reacted for 8 h; [2] Catalyst was added and reacted for 4 h; methyl oleate was added and reacted for 6 h

[0090] Example 2: Regeneration and recycling of SO3H-[C3N4]-MCR-3 b

[0091] SO3H-[C3N4]-MCR-3 obtained by centrifugation in Example 1 was sequentially washed with diethyl ether and deionized water, and then dried under vacuum at 60°C until a constant weight was achieved, thereby completing the regeneration. b

[0092] In a quartz photo-reactor flask equipped with magnetic stirring and circulating cooling water, 10 mg of regenerated SO3H-[C3N4]-MCR-3 was sequentially added b ​​, 20 ml of deionized water, 3 ml of ethanol, open stirring, mixture under 300 W xenon lamp light source (with 420 nm filter) irradiation, continuous bubbling into the air reaction 2 h. Add 12 ml of methyl oleate, keep the light source irradiation, continuous bubbling into the air reaction 6 h. Stand and separate phase, centrifugal separation of catalyst, organic phase is dried with anhydrous magnesium sulfate, suction filtration to obtain the target product. The first cycle using EMO yield 92.5%, the second cycle using EMO yield 91.4%, the third cycle using EMO yield 90.8%.

[0093] The above description is only the preferred embodiment of the present application, any equivalent changes and modifications made according to the scope of the patent application of the present application shall be within the scope of the present application.

Claims

1. Use of a sulfonic acid group functionalized C3N4 catalyst, characterized in that: The sulfonic acid group functionalized C3N4 catalyst is used as a heterogeneous visible light catalyst, air is used as an O2 source, and under the conditions of room temperature, normal pressure, neutral reaction, and visible light irradiation, methyl oleate is photo-catalyzed to synthesize epoxy methyl oleate; the sulfonic acid group functionalized C3N4 catalyst is covalently bonded to the N atom of the active amino group in the C3N4 molecular structure, the introduction of the sulfonic acid group enables the functionalized C3N4 to have photo-catalytic oxidation activity, Brønsted acid catalytic activity, and good surface amphiphilic activity, and the Brønsted acid catalytic site and the photo-catalytic site are spatially separated; the sulfonic acid group functionalized C3N4 catalyst has a nanosheet layer accumulation morphology; the sulfonic acid group functionalized C3N4 catalyst is synthesized by using dicyandiamide or melamine or melamine cyanurate and ammonium persulfate or potassium persulfate or tetrabutylammonium persulfate as precursors, and ammonium chloride or ammonium oxalate as a gas phase template, and then performing a thermal polycondensation reaction.

2. Use of a sulfonic acid-functionalized C3N4 catalyst according to claim 1, characterized in that: The synthesis of the sulfonic acid group functionalized C3N4 catalyst includes the following steps: dicyandiamide or melamine or melamine cyanurate, ammonium persulfate or potassium persulfate or tetrabutylammonium persulfate, and ammonium chloride or ammonium oxalate are mixed and ground, then placed in an atmosphere box-type muffle furnace, continuously introduced with nitrogen, the heating rate is controlled to be 1.2-2.5 ℃ / min, heated to 500-650 ℃, and reacted for 3-5 h; the crude product is sufficiently ground, washed with deionized water and ethanol, and vacuum dried to a constant weight to obtain the target product.

3. Use of a sulfonic acid functionalized C3N4 catalyst according to claim 1, characterized in that: Specifically comprising the following steps: in a quartz photo-reactor bottle equipped with magnetic stirring, 10 mg of sulfonic acid functionalized C3N4 catalyst, 20 ml of ion-free water, 3 ml of ethanol are sequentially added, the stirring is started, the mixture is irradiated under 300 W xenon lamp or 60 W LED lamp, and continuously bubbled with air for 2-4 h, 12 ml of methyl oleate is added, the light source is kept on, continuously bubbled with air for 4-6 h, and then phase separation is carried out by standing and centrifugation. The catalyst is separated by centrifugation, and the organic phase is dried with anhydrous magnesium sulfate and filtered to obtain the target product methyl epoxy oleate, with a yield of 74.6-93.2%, an iodine value of 2.5-3.1 g I2 / 100 g, and a color number （Pt-Co） <150, reaching the first-grade product index of methyl epoxy oleate.

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