Method for treating phenol-containing wastewater by photo-thermal synergistic normal-pressure wet air oxidation

Abstract

The present application belongs to the technical field of organic wastewater treatment, and particularly relates to a method for treating phenolic wastewater by photo-thermal synergistic normal-pressure wet air oxidation. The method for treating phenolic wastewater by photo-thermal synergistic normal-pressure wet air oxidation mixes a catalyst and phenolic wastewater in a normal-pressure reaction container, irradiates the phenolic wastewater by using a visible light or ultraviolet light source, applies an external heat source to the phenolic wastewater, and blows air into the phenolic wastewater by an air pump to oxidize and degrade phenolic compounds in the wastewater. The method for treating phenolic wastewater by photo-thermal synergistic normal-pressure wet air oxidation has the advantages of low cost, high photo quantum efficiency, good oxidation degradation effect, and strong recycling usability. The method has excellent oxidation degradation efficiency for various phenolic compounds in wastewater, and has high universality and popularization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of organic wastewater treatment, and particularly relates to a method for treating phenolic wastewater by photo-thermal synergistic normal-pressure wet air oxidation. BACKGROUND

[0002] Phenolic compounds belong to the prototype toxic substances, and have toxic effects on all living organisms. Coking plants, oil refineries, plastic plants, resin plants, synthetic fiber plants and petrochemical plants and other enterprises involve the use of a large amount of phenolic compounds, and have become the main source of phenolic wastewater. Phenolic wastewater not only seriously threatens human health, but also harms animals and plants. When the content of phenol in water exceeds 1 ppm, it will cause a large number of fish to die; using phenolic wastewater to irrigate farmland will also cause a large area of crops to reduce yield or die. The content of phenolic compounds is an important indicator of water pollution, so its discharge standard must be strictly controlled.

[0003] At present, the main methods for treating phenolic wastewater include adsorption, extraction, biochemical method, Fenton method, ozone oxidation method, photocatalytic oxidation method and wet air catalytic oxidation method. The adsorption method has the problem of difficult desorption, and produces a large amount of solid hazardous waste; the extraction method needs to use organic extractant, which is easy to cause secondary pollution; the biochemical method has high requirements for wastewater quality, and is not suitable for high-concentration, high-salinity and biologically inhibited wastewater; the Fenton method and the ozone oxidation method use H2O2 and O3 as oxidants respectively, and the cost of the oxidants is high, so they are not suitable for high-concentration wastewater; the photocatalytic oxidation method simply uses the holes induced by light to oxidize and degrade organic matter, and due to the low light quantum efficiency, it is only suitable for low-concentration wastewater. The wet air catalytic oxidation method is currently the method with the lowest running cost for treating high-concentration wastewater. However, this method requires high temperature and high pressure conditions, in order to meet the corrosion resistance requirements, the one-time investment of the equipment is large, and there is a safety hazard. Therefore, in order to solve the problems of the prior art, it is urgent to explore a wet air catalytic oxidation treatment method which can efficiently degrade phenolic compounds under non-high-temperature and normal-pressure conditions.

[0004] Chinese invention patent CN201810297664.7 discloses a composite photocatalyst for treating phenolic wastewater, and a preparation method and application thereof. The degradation rate of phenol can reach 24.6% to 94.8% after one hour of illumination by using molecular sieve loaded with calcium titanate as a photocatalyst, but there is a lack of interaction between the molecular sieve and the calcium titanate, the calcium titanate powder is easy to fall off, and the catalyst is easy to agglomerate in water, and the catalyst has poor reusability.

[0005] Chinese invention patent CN202111441003.5 discloses a method for degrading organic pollutants by transition metal phosphide and photocatalytic self-produced hydrogen peroxide. The method utilizes the unique self-produced H2O2 capacity and photocatalytic capacity of transition metal phosphide to degrade organic pollutants, but it needs to introduce soluble iron salt as a catalyst for decomposing H2O2, and the treated water may have color; Fe 2+ Reaction with H2O2 reduces the utilization rate of H2O2, and the treatment effect is limited by the pH value of the wastewater (pH = 2-5), which to some extent affects the popularization and application of the method.

[0006] Chinese invention patent CN202110757870.3 discloses a method for photocatalytic production of H2O2 without sacrificial agent. Hydrothermal carbon is used as a photocatalyst, which is dispersed in water, oxygen is introduced and maintained in a saturated state, and then H2O2 is obtained by irradiation with a visible light source. However, the band gap energy of hydrothermal carbon light is high, and the conductivity is poor, resulting in low quantum efficiency.

[0007] In summary, coupling photocatalytic oxygen reduction to produce H2O2 with Fenton-like reaction and applying it to wet air catalytic oxidation process can not only solve the high cost problem caused by using H2O2 as oxidant in Fenton method, but also effectively avoid the high temperature and high pressure operating conditions required by traditional wet air catalytic oxidation method. SUMMARY

[0008] The purpose of the present application is to provide a method for treating phenolic wastewater by photo-thermal synergistic normal pressure wet air oxidation. The method has the advantages of mild operating conditions, low equipment investment, low running cost, high treatment efficiency and wide application range, and can efficiently oxidize and degrade various phenolic compounds to generate carbon dioxide and water, effectively reducing the chemical oxygen demand value of phenolic wastewater.

[0009] The method for treating phenolic wastewater by photo-thermal synergistic normal pressure wet air oxidation disclosed in the present application mixes the catalyst and phenolic wastewater in a normal pressure reaction vessel, irradiates the phenolic wastewater with a visible light or ultraviolet light source, and applies an external heat source to the phenolic wastewater, and blows air into the phenolic wastewater through an air pump to oxidize and degrade phenolic compounds in the wastewater; the catalyst includes a carbon nitride carrier and a metal active center loaded thereon; wherein the carbon nitride carrier is one of alpha-phase carbon nitride, beta-phase carbon nitride, graphite-phase carbon nitride, cubic-phase carbon nitride or quasi-cubic-phase carbon nitride; the metal active center is at least one of Cu, Fe, Ce, Co, Mn, Ti, Zr, Mo or Zn, and the metal active center is in a monatomic dispersed state; the mass of the metal active center accounts for 0.1-20% of the mass of the carbon nitride carrier.

[0010] Among them:

[0011] Preferably, the carbon nitride support is graphite-phase carbon nitride; the metal active center is Cu; the mass of the metal active center accounts for 5% of the mass of the carbon nitride support.

[0012] The metal active center precursor is one of Cu-, Fe-, Co-, Mn-, Ce-, Ti-, Zr-, Mo- or Zn-based nitrate, acetate, sulfate, chloride or phthalocyanine compound; preferably, the metal active center precursor is metal nitrate.

[0013] The metal active center has strong metal-support interaction with the carbon nitride support, and the metal active center (M) forms at least one of MN1 coordination chemical bond, MN2 coordination chemical bond, MN3 coordination chemical bond or MN4 coordination chemical bond with the nitrogen (N) atom in the carbon nitride support; preferably, the metal active center forms MN4 coordination chemical bond with the nitrogen atom in the carbon nitride support.

[0014] The phenolic compound in the phenolic wastewater is at least one of phenol, p-phenol, m-cresol, benzenediol, nitrophenol, chlorophenol, guaiacol or phenyl ether.

[0015] The COD value of the phenolic wastewater is 100-200,000 mg / L.

[0016] The mass ratio of the catalyst to the phenolic wastewater is 0.1%-20%.

[0017] The wavelength range of the visible light or ultraviolet light source is 200-600 nm.

[0018] The external heating source is one of electric heating, steam heating or heat conducting oil heating, and the heating temperature range of the external heating source is 40-100°C.

[0019] The air pump blows air into the phenolic wastewater at a rate of 0.5-20 L / min.

[0020] The oxidation degradation time is 3-4 h.

[0021] The preparation method of the catalyst comprises the following steps:

[0022] (1) The nitrogen-containing compound is calcined under inert atmosphere by programmed temperature rising to a certain temperature, and then cooled to obtain bulk carbon nitride (sample 1);

[0023] (2) The bulk carbon nitride is impregnated with intercalation molecular solution, and then subjected to ultrasonic treatment, stirring, evaporation, grinding, programmed temperature calcination under inert atmosphere and cooling under inert atmosphere to obtain layered carbon nitride (sample 2);

[0024] (3) The layered carbon nitride is impregnated with a metal active center precursor solution, and then subjected to ultrasonic treatment, stirring, evaporation and grinding to obtain a pre-catalyst (sample 3);

[0025] (4) calcining the pre-catalyst under an inert atmosphere at a programmed temperature to a certain temperature, then cooling, to obtain a catalyst for treating phenol-containing wastewater by photo-thermal synergistic normal-pressure wet air oxidation.

[0026] wherein:

[0027] The nitrogen-containing compound in step (1) is at least one of urea, aminoacetonitrile, dicyanediamine, melamine, guanidine hydrochloride, aminoguanidine hydrochloride or choline chloride; preferably, the nitrogen-containing compound is melamine.

[0028] The inert atmosphere in step (1), step (2) and step (4) is one of nitrogen, argon or helium; preferably, the inert atmosphere is nitrogen.

[0029] The programmed temperature in step (1) is from room temperature to 390°C at a temperature increasing rate of 2°C / min, keeping for 1 h, then to 520°C at a temperature increasing rate of 2°C / min, keeping for 2 h.

[0030] The cooling in step (1) is natural cooling to room temperature in the inert atmosphere.

[0031] The intercalation molecule in step (2) is at least one of ammonium chloride, ammonium nitrate or ammonium carbonate; preferably, the intercalation molecule is ammonium chloride.

[0032] The intercalation molecule in step (2) is 0.02 mol per gram of bulk cubic carbon nitride.

[0033] The ultrasonic temperature in step (2) is room temperature, the ultrasonic time is 0.5-5 h; the stirring temperature is room temperature, the stirring time is 0.5-5 h; the evaporation temperature is 60-100°C, and the evaporation time is 5-10 h.

[0034] The particle size is controlled to be 50-500 mesh by grinding in step (2).

[0035] The programmed temperature in step (2) is from room temperature to 390°C at a temperature increasing rate of 2°C / min, keeping for 1 h.

[0036] The cooling in step (2) is natural cooling to room temperature in the inert atmosphere.

[0037] The metal active center precursor in step (3) is 0.8 mmol per gram of layered cubic carbon nitride.

[0038] The ultrasonic temperature in step (3) is room temperature, the ultrasonic time is 0.5-5 h; the stirring temperature is room temperature, the stirring time is 0.5-5 h; the evaporation temperature is 60-100°C, and the evaporation time is 5-10 h.

[0039] The particle size is controlled by grinding in step (3) to be 50-500 mesh.

[0040] The temperature is raised from room temperature to 300℃ at a rate of 2℃ / min and kept for 1h in step (4).

[0041] The temperature is lowered to room temperature naturally in an inert atmosphere in step (4).

[0042] Compared with the prior art, the present application has the following advantages:

[0043] (1) The method for treating phenol-containing wastewater by photo-thermal synergistic normal-pressure wet air oxidation, which applies visible light or ultraviolet light irradiation and an external heat source to the phenol-containing wastewater simultaneously through the action of a catalyst, effectively oxidizes and degrades phenolic compounds to carbon dioxide and water by using H2O2 generated by the photocatalytic reduction of oxygen in the air. The method has mild operating conditions (normal pressure, temperature <100℃), low equipment investment, low operating cost, high treatment efficiency (COD removal rate >99%), and wide application range (acidic, neutral, alkaline, and high-salt wastewater), which can not only solve the high treatment cost problem caused by using H2O2 as the oxidant in the Fenton method, but also avoid the high temperature and high pressure operating conditions required by the traditional wet air catalytic oxidation method.

[0044] (2) The catalyst used in the method for treating phenol-containing wastewater by photo-thermal synergistic normal-pressure wet air oxidation has a coordination chemical bond between the metal active center and the nitrogen atom in the carbon nitride carrier. The strong Lewis basicity of the nitrogen atom enhances the electron density of the metal active center, which is beneficial to the adsorption and activation of oxygen molecules and improves the generation efficiency of H2O2. The metal active center in the catalyst is in a monatomic dispersed state, and the utilization efficiency of the metal atom is 100%. The coordination chemical bond between the metal active center and the nitrogen atom in the carbon nitride carrier has a strong metal-carrier interaction, and there is no problem of metal active center loss, so the catalyst has a long service life.

[0045] (3) The catalyst used in the method for treating phenol-containing wastewater by photo-thermal synergistic normal-pressure wet air oxidation catalyzes the generation of photo-generated electrons and photo-generated holes under visible light or ultraviolet light induction. The photo-generated electrons reduce oxygen in the air to generate H2O2, and further decompose H2O2 to generate hydroxyl radicals (·OH), which effectively oxidize and degrade phenolic compounds. No additional soluble iron salt is needed as a catalyst for decomposing H2O2, and the method has a wide pH value application range for wastewater. The photo-generated holes can also directly oxidize and degrade phenolic compounds, inhibit the recombination of photo-generated electrons and photo-generated holes, and have high photo quantum efficiency.

[0046] (4) The method for treating phenolic wastewater by photo-thermal synergistic normal-pressure wet air oxidation, which adopts a catalyst preparation method with simple process, convenient operation and low cost, can realize large-scale and batch production, and is conducive to industrial application.

[0047] (5) The method for treating phenolic wastewater by photo-thermal synergistic normal-pressure wet air oxidation has the advantages of low cost, high light quantum efficiency, good oxidation degradation effect and strong recycling performance, and has excellent oxidation degradation efficiency on various phenolic compounds in wastewater, and has high universality and popularization. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a high-resolution spherical aberration-corrected transmission electron microscopy image of the Cu / g-C3N4 catalyst prepared in Example 1;

[0049] Figure 2 is a synchrotron X-ray absorption spectrum of the Cu / g-C3N4 catalyst prepared in Example 1. DETAILED DESCRIPTION

[0050] The application will be further described below in combination with examples.

[0051] Example 1

[0052] The method for treating phenolic wastewater by photo-thermal synergistic normal-pressure wet air oxidation described in this embodiment 1 adds 0.5 g of catalyst (Cu / g-C3N4) to 50 mL of 6 g / L phenol solution (COD = 14000 mg / L), places the reaction system in a dark room, irradiates the phenol solution with a xenon lamp with a 420 nm filter, heats the phenol solution to 80℃ at the same time, and uses an air pump to blow air into the phenol solution at a flow rate of 1 L / min, and reacts for 4 h. 2 mL of the reaction system is sampled at intervals, and the COD value of the phenol solution is determined and analyzed.

[0053] The catalyst (Cu / g-C3N4) used therein includes a carbon nitride carrier and an atomically dispersed state of metal active centers supported thereon, and there is a strong metal-support interaction between the metal active centers and the carbon nitride carrier.

[0054] Among them:

[0055] The carbon nitride carrier in the catalyst is a graphite phase carbon nitride (g-C3N4) carrier.

[0056] The metal active center in the catalyst is Cu.

[0057] The mass of Cu in the catalyst accounts for 5 wt.% of the mass of the graphite phase carbon nitride carrier.

[0058] The Cu in the catalyst is in an atomic dispersion state (characterized by high-resolution spherical aberration-corrected transmission electron microscopy, see Figure 1 ).

[0059] The metal-support interaction in the catalyst is that the Cu forms a CuN4 coordination chemical bond with the nitrogen atoms in the graphite phase carbon nitride support (characterized by synchrotron radiation X-ray absorption spectroscopy, see Figure 2 ).

[0060] The preparation method of the catalyst for treating phenolic wastewater by photo-thermal synergistic atmospheric wet air oxidation in the embodiment 1 is composed of the following steps:

[0061] (1) Put 12 g of melamine in a tube furnace, control the nitrogen flow rate to be 30 mL / min, the heating rate to be 2 ℃ / min, heat from room temperature to 390 ℃ and keep for 1 h, continue to heat to 520 ℃ and keep for 2 h, and naturally cool to room temperature under nitrogen atmosphere to obtain bulk graphite phase carbon nitride (sample 1).

[0062] (2) Dissolve 6 g of ammonium chloride in 30 mL of water, add 6 g of sample 1, ultrasonic treat for 1 h, stir at room temperature for 5 h, evaporate the solvent in an oil bath at 80 ℃ (the evaporation time is 6 h), and grind (control the particle size to be 200 mesh by grinding) and then put it in a tube furnace, control the nitrogen flow rate to be 30 mL / min, the heating rate to be 2 ℃ / min, heat from room temperature to 390 ℃ and keep for 1 h, and naturally cool to room temperature under nitrogen atmosphere to obtain layered graphite phase carbon nitride (sample 2).

[0063] (3) Dissolve 1.15 g of Cu(NO3)2·3H2O in 30 mL of water, add 6 g of sample 2, ultrasonic treat at room temperature for 1 h, stir at room temperature for 5 h, evaporate the solvent in an oil bath at 80 ℃ (the evaporation time is 6 h), and grind (control the particle size to be 200 mesh by grinding) to obtain sample 3.

[0064] (4) Put 6 g of sample 3 in a tube furnace, control the nitrogen flow rate to be 30 mL / min, the heating rate to be 2 ℃ / min, heat from room temperature to 300 ℃ and keep for 1 h, and naturally cool to room temperature under nitrogen atmosphere to obtain the Cu / g-C3N4 catalyst for treating phenolic wastewater by photo-thermal synergistic atmospheric wet air oxidation.

[0065] Embodiments 2-9

[0066] The method for treating phenolic wastewater by photo-thermal synergistic atmospheric wet air oxidation in the embodiments 2-9 is the same as that in embodiment 1, and the catalysts used are also the same, and the difference lies in that the wavelengths of the light sources and the heating temperatures are different.

[0067] The COD removal effects of the phenol solutions corresponding to embodiments 1-9 are shown in Table 1.

[0068] COD removal effect of phenol solution under different light source wavelengths and heating temperatures

[0069]

[0070] As shown in Table 1, the shorter the wavelength of the light source, the higher the COD removal rate, and the light in the visible light region has the highest efficiency; the higher the heating temperature of the phenol solution, the higher the degree of activation of the organic molecules, and the higher the COD removal efficiency. It is appropriate to control the heating temperature at 80°C under normal pressure.

[0071] Examples 10-20

[0072] The method for treating phenol-containing wastewater by the photo-thermal synergistic normal pressure wet air oxidation described in Examples 10-20 is the same as that in Example 1, except that the air flow rate, catalyst dosage and reaction time are different.

[0073] The COD removal effect of the phenol solution corresponding to Examples 10-20 is shown in Table 2.

[0074] Table 2 COD removal effect of phenol solution under different air flow rates, catalyst dosages and reaction times

[0075]

[0076]

[0077] As shown in Table 2, the higher the air flow rate, the more oxygen provided to the reaction system, and the higher the COD removal rate; the larger the catalyst dosage, the higher the efficiency of oxidizing and degrading organic matter; and the longer the reaction time, the higher the COD removal rate.

[0078] Examples 21-26

[0079] The method for treating phenol-containing wastewater by the photo-thermal synergistic normal pressure wet air oxidation described in Examples 21-26 is the same as that in Example 1, except that the types of phenolic compounds in the simulated wastewater are different.

[0080] The COD removal effect of different phenolic compound solutions corresponding to Examples 21-26 is shown in Table 3.

[0081] Table 3 COD removal effect of different phenolic compound solutions

[0082]

[0083] As shown in Table 3, the method and catalyst for treating phenol-containing wastewater by the photo-thermal synergistic normal pressure wet air oxidation have excellent oxidizing and degrading effect on various phenolic compounds in the simulated wastewater, and the COD removal rate can reach 99%.

[0084] Examples 27-37

[0085] The method for treating phenol-containing wastewater by photo-thermal synergistic normal-pressure wet air oxidation described in Examples 27-37 is the same as that in Example 1, except that the types and contents of the metal active centers in the catalyst and the types of the precursors of the metal active centers are different.

[0086] The COD removal effects of the phenol solutions corresponding to Examples 27-37 are shown in Table 4.

[0087] Table 4 COD removal effects of phenol solutions using different types and contents of metal active centers and different types of precursors

[0088]

[0089]

[0090] As can be seen from Table 4, the Cu metal active center has the best effect on the oxidative degradation of phenol; the COD removal rate has a volcano-type distribution with the Cu loading amount in the catalyst, and the COD removal rate is the highest when the Cu loading amount is 5 wt.%; the type of Cu precursor has an effect on the oxidative degradation of phenol, and the effect is the best when Cu(NO3)2 is used.

[0091] Examples 38-46

[0092] The method for treating phenol-containing wastewater by photo-thermal synergistic normal-pressure wet air oxidation described in Examples 38-46 is the same as that in Example 1, except that the types of the nitrogen-containing compounds used to prepare the graphite-phase carbon nitride are different.

[0093] The COD removal effects of the phenol solutions corresponding to Examples 38-46 are shown in Table 5.

[0094] Table 5 COD removal effects of phenol solutions using catalyst supports prepared by thermal polymerization of different nitrogen-containing compounds

[0095]

[0096] As can be seen from Table 5, the type of the nitrogen-containing compound used to prepare the catalyst support of carbon nitride also has an effect on the oxidative degradation of phenol, and the catalyst synthesized using carbon nitride prepared by thermal polymerization of melamine as the support has the highest efficiency in the oxidative degradation of phenol.

Claims

1. A method for treating phenolic wastewater by photo-thermal synergistic atmospheric wet air oxidation, characterized in that: The catalyst and phenolic wastewater are mixed in a normal pressure reaction container, the phenolic wastewater is irradiated by a visible light or ultraviolet light source, an external heating source is applied to the phenolic wastewater, air is pumped into the phenolic wastewater by an air pump to oxidize and degrade phenolic compounds in the wastewater; the catalyst comprises a carbon nitride carrier and a metal active center loaded on the carbon nitride carrier; the carbon nitride carrier is graphite phase carbon nitride; the metal active center is Cu; the metal active center is in a monatomic dispersion state; the mass of the metal active center accounts for 5% of the mass of the carbon nitride carrier; The preparation method of the catalyst comprises the following steps: (1) roasting a nitrogen-containing compound under an inert atmosphere by programmed temperature rising to a certain temperature, and then cooling to obtain a bulk carbon nitride; (2) impregnating the bulk carbon nitride with an intercalation molecule solution, and then performing ultrasonic treatment, stirring, evaporation, grinding, programmed temperature roasting under an inert atmosphere, and cooling under an inert atmosphere to obtain a layered carbon nitride; (3) impregnating the layered carbon nitride with a metal active center precursor solution, and then performing ultrasonic treatment, stirring, evaporation, and grinding to obtain a pre-catalyst; (4) roasting the pre-catalyst under an inert atmosphere by programmed temperature rising to a certain temperature, and then cooling to obtain a catalyst for treating phenolic wastewater by normal pressure wet air oxidation with light-heat synergy; In the step (1), the nitrogen-containing compound is melamine; In the step (2), the intercalation molecule is ammonium chloride. The metal active center precursor is a Cu-based nitrate.

2. The method of treating phenolic wastewater by photo-thermal synergistic atmospheric wet air oxidation according to claim 1, characterized in that: The phenolic compounds in the phenolic wastewater are at least one of phenol, p-phenol, m-cresol, hydroquinone, nitrophenol, chlorophenol, guaiacol, or phenyl ether; 3. The method of treating phenolic wastewater by photo-thermal synergistic atmospheric wet air oxidation according to claim 1, characterized in that: The COD value of the phenolic wastewater is 100-200,000 mg / L; The mass ratio of the catalyst to the phenolic wastewater is 0.1-20%; The wavelength range of the visible light or ultraviolet light source is 420 nm. The external heating source is one of electric heating, steam heating, or heat conducting oil heating, and the heating temperature of the external heating source is 80°C; 4. The method of treating phenolic wastewater by photo-thermal synergic normal pressure wet air oxidation according to claim 1, characterized in that: The air pump pumps air into the phenolic wastewater at a rate of 1 L / min; The oxidation and degradation time is 4 h. The inert atmosphere in the steps (1), (2), and (4) is the same, and the inert atmosphere is one of nitrogen, argon, or helium; 5. The method of treating phenolic wastewater by photo-thermal synergistic atmospheric wet air oxidation according to claim 1, characterized in that: In the step (1), the programmed temperature rising is rising from room temperature to 390°C at a rate of 2°C / min for 1 h, and then rising to 520°C at a rate of 2°C / min for 2 h; In the step (1), the cooling is natural cooling to room temperature in an inert atmosphere. In the step (2), 0.02 mol of the intercalation molecule corresponds to each gram of the bulk carbon nitride; 6. The method of treating phenolic wastewater by photo-thermal synergic normal pressure wet air oxidation according to claim 1, characterized in that: In the step (2), the ultrasonic temperature is room temperature, the ultrasonic time is 0.5-5 h, the stirring temperature is room temperature, the stirring time is 0.5-5 h, the evaporation temperature is 60-100°C, and the evaporation time is 5-10 h; In the step (2), the particle size is controlled to be 50-500 mesh by grinding; In the step (2), the programmed temperature rising is rising from room temperature to 390°C at a rate of 2°C / min for 1 h; In the step (2), the cooling is natural cooling to room temperature in an inert atmosphere. ​ 7. The method of treating phenolic wastewater by photo-thermal synergic normal pressure wet air oxidation according to claim 1, characterized in that: 0.8 mmol of metal active center precursor per gram of layered carbon nitride in step (3); The ultrasonic temperature in step (3) is room temperature, and the ultrasonic time is 0.5-5 h; the stirring temperature is room temperature, and the stirring time is 0.5-5 h; the evaporation temperature is 60-100 °C, and the evaporation time is 5-10 hours; The particle size is controlled by grinding in step (3) to be 50-500 mesh.

8. The method of treating phenolic wastewater by photo-thermal synergic atmospheric wet air oxidation according to claim 1, characterized in that: The programmed temperature in step (4) is raised from room temperature to 300 °C at a rate of 2 °C / min and kept for 1 h; The cooling in step (4) is natural cooling to room temperature in an inert atmosphere.

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