CN111359650A

CN111359650A - Preparation method, product and application of iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst

Info

Publication number: CN111359650A
Application number: CN202010331486.2A
Authority: CN
Inventors: 马建青; 王丽艳; 张会宁; 钱勇兴; 靳慧霞; 张科锋
Original assignee: Ningbo Institute of Technology of ZJU
Current assignee: Ningbo Institute of Technology of ZJU
Priority date: 2020-04-24
Filing date: 2020-04-24
Publication date: 2020-07-03
Anticipated expiration: 2040-04-24
Also published as: CN111359650B

Abstract

The invention discloses a preparation method of an iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst, which comprises the following steps: dissolving iron salt, nickel salt and a graphite-phase carbon nitride precursor in a solvent, removing the solvent, and calcining the obtained solid to obtain an iron-nickel doped graphite-phase carbon nitride compound; and in the presence of a reducing agent, reacting the iron-nickel doped graphite-phase carbon nitride compound with a palladium catalyst to obtain the iron-nickel-palladium co-doped graphite-phase carbon nitride composite catalyst. The invention also discloses the catalyst prepared by the preparation method and an application method of the catalyst. The invention synthesizes hydrogen peroxide in situ at normal temperature and normal pressure by the interaction of Fe, Ni, Pd and graphite-phase carbon nitride to directly degrade pollutants.

Description

Preparation method, product and application of iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst

Technical Field

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method, a product and application of an iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst.

Background

With the continuous development of industrialization, the emission of various pollutants is increasing, and the health and the ecological environment of human beings are greatly threatened. Although the traditional biological treatment technology has low cost, the treatment effect on some refractory toxic substances is poor, and the water quality often cannot reach the standard and is discharged. The advanced oxidation technology is used as a new water treatment technology and has the characteristics of quick reaction, wide application range, no secondary pollution and the like. Wherein the hydrogen peroxide (H) is based on₂O₂) The Fenton technology has the advantages of simple and convenient operation, high efficiency, no toxic action on subsequent biochemical treatment, environmental friendliness and the like, but because of H₂O₂The self is not stable enough, and a large amount of side reactions also exist in the reaction process, so that H₂O₂Is less used, and in addition H₂O₂The price and the transportation and storage costs are also higher, which is not beneficial to being put into practical production and use. The in-situ synthesis technology has the characteristics of simple operation, low cost and the like, and can greatly improve H when being applied to the Fenton technology₂O₂And (4) utilization rate. Therefore, the technology has received a lot of attention.

In situ continuous synthesis of H using a suitable hydrogen source under suitable conditions₂O₂And then directly applied, so that ineffective decomposition thereof can be avoided and excessive H can be suppressed₂O₂The loss of the generated hydroxyl radical (. OH) can greatly increase H₂O₂The utilization rate and the treatment effect, thereby reducing the operation cost. Although the hydrogen content in formic acid is only 4.4 wt%, the hydrogen production performance of formic acid is superior to most other hydrogen-containing materials (such as formaldehyde, hydroxylamine, hydrazine, etc.). Hydrogen and H produced by formic acid under acidic or neutral condition₂The nature of the reaction of (a) is essentially the same. Formic acid can be regarded as a promising preparation H₂O₂The raw material of (2).

Graphitized carbon nitride (g-C)₃N₄) Is aA graphite-like material having a unique semiconductor band structure and stable chemical properties. The g-C can be synthesized by taking low-cost nitrogen-rich substances such as melamine, ammonium thiocyanate, urea, thiourea and the like as precursors through simple high-temperature heating₃N₄. As catalyst, pure g-C₃N₄The molecule has 6 sites comprising lone pair electrons and equivalent N atoms, and these sites are easy to form chemical bond with metal ion to reduce the metal ion separating out rate and raise the electron conducting rate. This property is beneficial to the degradation of pollutants and is suitable for the application in Fenton-like systems.

Disclosure of Invention

The invention provides a preparation method of an iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst, which is simple to operate, low in process cost, free of a large amount of waste water and the like in the preparation process, and easy to realize industrialization.

The invention also provides the iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst prepared by the method, and the catalyst has high degradation efficiency on organic pollutants and low use cost.

The invention also provides an application method for degrading organic pollutants in wastewater by using the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst, which has the advantages of simple steps and high degradation efficiency.

A preparation method of an iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst comprises the following steps: dissolving iron salt, nickel salt and a graphite-phase carbon nitride precursor in a solvent, removing the solvent, and calcining the obtained solid to obtain an iron-nickel doped graphite-phase carbon nitride compound; and in the presence of a reducing agent, reacting the iron-nickel doped graphite-phase carbon nitride compound with a palladium catalyst to obtain the iron-nickel-palladium co-doped graphite-phase carbon nitride composite catalyst.

As a further optimization, the preparation method of the iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst comprises the following steps:

(1) dissolving a graphite phase carbon nitride precursor in water, stirring after completely dissolving, adding iron salt and nickel salt, heating to evaporate water after completely dissolving again, and grinding to obtain powder I;

(2) calcining the powder I to obtain an iron and nickel doped graphite phase carbon nitride composite catalyst, and grinding to obtain powder II;

(3) and dispersing the powder II and a palladium catalyst in water, performing ultrasonic treatment, stirring, dropwise adding a sodium borohydride solution, and after the reaction is finished, placing the mixture in a vacuum drying oven to be dried to obtain the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst.

As a specific embodiment, a preparation method of an iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst comprises the following steps:

(1) adding dicyandiamide into water, placing the mixture on a magnetic stirrer for heating and stirring, adding ferric chloride hexahydrate and nickel chloride hexahydrate after the dicyandiamide is completely dissolved, stirring, heating and evaporating to remove water, and slightly grinding to obtain red powder;

(2) calcining the red powder in a muffle furnace to obtain an iron and nickel co-doped graphite phase carbon nitride composite catalyst, and grinding to obtain light brown powder;

(3) and weighing the light brown powder, adding palladium chloride in proportion, dispersing in an ultrapure water solution, performing ultrasonic treatment for 15min, and then placing in a magnetic stirrer while stirring and dropwise adding a sodium borohydride solution. After reacting for 60min, placing the mixture in a vacuum drying oven for drying to obtain brown powder.

In order to facilitate the dissolution of the graphite phase carbon nitride precursor, in the step (1), water can be heated first, and then the graphite phase carbon nitride precursor is added; or directly adding the graphite phase carbon nitride precursor into hot water. Preferably, the temperature of the hot water is 70 to 90 ℃, and more preferably 80 ℃. Preferably, the stirring time is 0.5 to 2 hours, and more preferably 1 hour.

In the step (1), the ferric salt and the nickel salt are respectively one or more of chloride, nitrate, phosphate and sulfate of iron and nickel. The graphite phase carbon nitride precursor is selected from one or more of dicyandiamide, urea, melamine and thiourea.

In the step (1), the total amount of the added iron salt/the total amount of the nickel salt is 0.1 to 0.5mmol/g, and more preferably 0.15 to 0.35mmol/g, relative to the graphite-phase carbon nitride precursor (such as dicyandiamide); still more preferably, it is further preferably 0.25 mmol/g. The conversion of fe (ii) to fe (iii) is relatively rapid in fenton reactions, and the conversion of fe (iii) to fe (ii) is extremely slow, which is also the rate-determining step of the reaction. The purpose of adding Ni is to accelerate the reduction cycle of Fe (III) to Fe (II) and improve the selectivity of the formic acid dehydrogenation reaction and enhance the degradation effect of the catalyst on pollutants.

In the step (1), the molar ratio of iron to nickel in the iron salt and the nickel salt is 0.5-2: 1. Further preferably 0.5-1.5: 1; more preferably 0.5 to 1: 1. The optimal selection is that the molar ratio of iron to nickel is 1:1, and the total amount of the added iron salt/the total amount of the nickel salt is 0.1-0.5 mmol/g relative to dicyandiamide.

The calcining temperature in the step (2) is 450-600 ℃, and the heating rate is 3-8 ℃/min. When the temperature is too low, the precursor is not sufficiently decomposed, so that the generated pore channel structure is less, and the specific surface area is small. However, when the calcination temperature is too high, the produced carbon nitride is also decomposed, and the activity of the catalyst is also small. Thus, in this study, the calcination temperature is preferably 550 ℃ and the temperature increase rate is preferably 5 ℃/min. In the step (2), the calcination time is 2.5 to 4 hours, and more preferably 3 hours.

In the step (3), the palladium catalyst is preferably palladium chloride. Palladium chloride is added in an amount of 0.025 to 0.1mmol/g, more preferably 0.075mmol/g, based on dicyandiamide. The palladium metal has stronger stability as noble metal, and the palladium surface can absorb oxygen without dissociation, thus being beneficial to generating H by combining with hydrogen generated in the formic acid dehydrogenation reaction for catalytic reaction₂O₂。

In the step (3), a sodium borohydride solution is dripped to reduce Pd (II) into Pd (0), and the concentration of the added sodium borohydride solution is 1.5-3.0 mol/L, and is preferably 2 mol/L; the adding amount of the sodium borohydride solution is 20-40 mL, and the adding amount of the sodium borohydride is 0.01-0.04 mol/g relative to the precursor. The Pd is uniformly dispersed in the iron and nickel co-doped graphite phase carbon nitride composite catalyst by ultrasonic treatment for 10-30 min, so that the contact area of the reaction is increased, and the utilization rate of the metal is improved.

Integrating the step (1), the step (2) and the step (3), wherein the optimal scheme is that the total amount of the added iron salt/the total amount of the nickel salt is 0.25mmol/g relative to dicyandiamide; the calcination temperature is 550 ℃; the calcination time was 3 hours. The total amount of palladium chloride added was 0.075mmol/g relative to dicyandiamide.

The invention also provides the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst prepared by the preparation method of any one of the technical schemes.

The invention also provides an application method for degrading organic pollutants in wastewater by using the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst.

The iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst is used, and the catalyst is directly put into wastewater to be treated, so that the operation is very simple.

Preferably, the concentration of the organic pollutants in the wastewater is 10-800 mg/L; further preferably 10 to 300 mg/L.

Preferably, in the application process, the using amount of the catalyst is 1-3 g/L, and further preferably 2 g/L. The mass ratio of the catalyst to the pollutant is 10-50: 1; further preferably 10-20: 1.

Preferably, formic acid needs to be added in the process of degrading organic pollutants in wastewater by using the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst, wherein the molar concentration of the formic acid is preferably 20-50 mmol/L, and more preferably 40-50 mmol/L; still more preferably 46.6 mmol/L.

Experiments show that under the preferable conditions, the catalyst has extremely high catalytic removal effect on dye pollutants (one or more of AR-73 and tetracycline hydrochloride), and reaches more than 91% within 150 min.

Blowing air in the experiment with the flow rate of 100-500 mL/min, and preferably 100-300 mL/min; as a specific embodiment, the flow rate of the blowing air in the experiment was 200 mL/min.

The organic contamination comprises one or more of dye AR 73 and tetracycline hydrochloride.

The mechanism of the catalytic activity of the catalyst of the invention in combination with in situ synthesis of hydrogen peroxide and fenton-like technology may be as follows:

through XRD and FTIR, Fe and Ni are not found in the form of crystal particles. XPS technology high resolution spectrum further analyzes that Fe mainly exists in the composite catalyst in a Fe-N and Fe-O coordination form; ni exists in the composite catalyst mainly in a Ni-N and Ni-O coordination form; pd is mainly present in the form of crystalline particles of Pd (0), and secondly in the form of Pd-O coordination in the composite catalyst. The coordination of Fe and Ni with N respectively facilitates the formation of two intermetallic synergy effects through electron conduction of graphite phase carbon nitride. Ni also acts to increase the selectivity of the formic acid dehydrogenation reaction. The uniform distribution of the zero-valent palladium increases the contact area for adsorbing oxygen and hydrogen and electron transfer.

The formic acid is dehydrogenated under the action of catalyst, and the hydrogen produced at the same time and oxygen in the air are reacted under the action of catalyst to form H₂O₂. Subsequently, OH generated by Fe (II) degrades organic pollutants. Fe. The interaction among Ni, Pd and graphite-phase carbon nitride ensures that the obtained composite catalyst has good Fenton-like catalytic performance.

The capture of OH during the reaction by lutidine N-oxide (DMPO) and detection by paramagnetic resonance confirmed that OH is the major oxidative species. During the reaction, the Fe-N and Ni-N on the surface of the composite catalyst continuously undergo the circulation of Fe (III) and Fe (II) under the synergistic action, and catalyze H₂O₂OH is generated, and meanwhile, organic matters in the solution move to the surface of the catalyst and are attacked by the OH to be degraded.

The iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst disclosed by the invention is rapid and efficient in catalytic degradation of the dye AR-73, and also has good catalytic activity on organic matters such as tetracycline hydrochloride and the like.

When the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst is used, the catalyst is directly put into wastewater to be treated, so that the operation is very simple, and the catalyst has great practical value.

Drawings

FIG. 1(a) is an XRD pattern spectrum and (b) is a Fourier infrared change spectrum of the catalysts prepared in comparative examples 1 and 2 and example 1;

FIG. 2(a) shows XPS spectra of catalysts prepared in comparative examples 1 and 2 and example 1, and (b) to (f) show XPS spectra and analyses thereof of catalysts prepared in example 1 ((b) C1 s, (C) N1 s, (d) Ni 2p, (e) Fe 2p, (f) Pd 3 d).

Fig. 3(a) and (b) are SEM images of the catalyst prepared in example 1 ((a) is an overall view of the sample, (b) is a result view for conveniently observing that the pores of the sample appear clustered as if after metal precipitation), (c) (d) is an HRTEM view of the catalyst prepared in example 1;

FIG. 4(a) is a graph showing the degradation curves of the catalysts prepared in examples 1 to 4 and comparative examples 1 to 2 with respect to tetracycline hydrochloride; (b) the degradation curves of the FeNi-Pd @ CN (1: 1) prepared in example 1 on the acid red 73 and the degradation curves of the FeNi-Pd @ CN (1: 1) without blowing air or adding formic acid on the acid red 73;

FIG. 5 is a comparison of the XRD patterns of FeNi-Pd @ CN after recycle and freshly made FeNi-Pd @ CN in Performance test example 3;

FIG. 6(a) shows the performance test in example 6 using DMPO capture (. OH) and methanol capture (. O)₂ ^-) Paramagnetic resonance detection spectra. (b) The curves (c) for comparing the amounts of hydrogen peroxide generated in the experiments with Fe or Ni alone or without or with benzoquinone added in Performance test 5 are curves for the amounts of hydrogen peroxide generated in the experiments with isopropanol and with benzoquinone added, respectively, in Performance test 6.

Detailed Description

The invention is further illustrated by the following examples:

the examples used the starting materials:

dicyandiamide (CP, 98%), ferric chloride hexahydrate (AR, 99.0%), nickel chloride hexahydrate (AR, 99.0%), palladium chloride (AR, 59-60%), formic acid (AR, 88%). Acid Red 73(AR-73) was purchased from Doctoria chemical Co., Ltd. Tetracycline hydrochloride (TC) was purchased from Shanghai Aladdin Biotechnology Ltd. The experimental water is deionized water.

Examples 1 to 4

Adding 50mL of deionized water into a 100mL beaker, heating to 80 ℃ by using a heater with a temperature control function, adding 2g of dicyandiamide, magnetically stirring until the dicyandiamide is completely dissolved, then adding a certain amount of ferric chloride hexahydrate and nickel chloride hexahydrate according to the data in the table 1, and continuously stirring for 1 h. Heating to 80 deg.C in a common oven, and stirring until water is completely evaporated. Slightly grinding the mixture to obtain brown powder, and calcining in a muffle furnace at 550 ℃ for 3h at the heating rate of 5 ℃/min. Taking out and grinding to obtain light brown powder. Weighing the balance, adding palladium chloride in proportion, dispersing in ultrapure water (30mL) for 15min by ultrasonic wave, and then placing in a magnetic stirrer, and dropwise adding 2 mol/L30 mL sodium borohydride solution while stirring. After reacting for 60min, placing the mixture in a vacuum drying oven for drying to obtain the brown powder composite catalyst which is expressed by FeNi-Pd @ CN.

TABLE 1 preparation conditions of examples 1 to 4

Comparative examples 1 to 3

Comparative examples 1 to 3 were prepared according to the preparation methods of examples, in which the amounts of ferric chloride hexahydrate and nickel chloride hexahydrate were added as shown in table 2, and the obtained products were represented by the following symbols, respectively: Ni-Pd @ CN (comparative example 1), Fe-Pd @ CN (comparative example 2).

TABLE 2 preparation conditions for comparative examples 1 to 3

Characterization of the catalyst 1

The XRD and fourier-infrared change patterns of the catalysts prepared in example 1 and comparative examples 1 and 2, respectively, are determined, and are shown in fig. 1. It can be seen from the data change of the two spectra (see fig. 1) that the catalysts prepared in examples 1 to 3 all retain the graphite phase carbon nitride peak (see fig. 3(a)), but the peak intensity is weakened and widened, which indicates that the original layer structure is destroyed and certain agglomeration occurs to form adsorption pores, which can also be shown in fig. 3 (b). This is another reason for the reduction in specific surface area. Table 3 shows the specific area test results, and it can be seen visually that the simultaneous doping of Fe and Ni metals significantly reduces the surface area of the catalyst, but also increases the electron conduction distance between the metals, which is beneficial to the electron transfer and thus improves the activity of the catalyst.

TABLE 3 comparison of specific surface areas of example 1 and comparative examples 1 to 2

Sample (I)	Specific surface area (m)²/g)
		Comparative example 1	14.40155
Example 1	9.18082
		Comparative example 2	11.26370

Characterization of the catalyst 2

XPS full spectrum scans of the products prepared in example 1 and comparative examples 1 and 2 (see fig. 2(a)) indicate the surface of the Fe, Ni, Pd doped or deposited graphite phase carbon nitride. In the present study, the graphite phase carbon nitride, Fe, Ni and Pd interact with each other, thereby contributing to the catalyst to obtain higher catalytic activity. The concrete expression is as follows:

(1) fig. 1 in conjunction with fig. 3(a) and (b) can speculate that the catalyst deforms while substantially maintaining the layered morphology of the graphite phase carbon nitride and obvious adsorption pores appear, indicating that the three are not simply physically mixed. The high temperature calcination causes the doping of the metal into the structure to destroy the original structure forming internal pores.

(2) In XPS elemental high resolution scans (see fig. 2(b) -2 (f)) of the product prepared in example 1, fig. 2(b) and 2(c) together demonstrate that C, N the chemical bond combinations of the two elements correspond to the full chemical bond combination of graphite phase carbon nitride; the analysis in FIG. 2(d) reveals that most of the iron exists in the form of ferrous iron. FIG. 2(e) shows that Ni is embedded in the carbon nitride lattice in a coordinated manner. The XRD pattern of fig. 1(a) does not find the presence of iron and nickel in crystalline form, and thus it is judged that Fe and Ni should be present in the complex mainly in coordinated form. The XPS technology is utilized to confirm that Fe and Ni exist mainly in the form of Fe-N and Fe-O coordination and Ni-N and Ni-O coordination (figure 2(d) and figure 2 (e)); FIG. 2(f) demonstrates that a portion of the crystalline form of Pd metal is present. While there is a significant metal precipitation phenomenon in fig. 3(c), the results of the pitch measurement in fig. 3(d) sufficiently confirm that a part of Pd metal is stored in the carbon nitride structure in a zero valence state, and another part is present in the form of Pd — O in conjunction with fig. 2 (f).

Testing of catalyst Performance

The catalytic degradation experiment was carried out in a 250mL beaker at ambient temperature and pressure, and the contaminant was acid Red 73(AR-73) at a concentration of 200mg/L (100 mL). The amount of the catalyst added was 2g/L and the amount of formic acid added was 46.6mmol/L, and after a certain time interval, the reaction mixture was taken out and filtered through a 0.45 μm membrane to remove the catalyst, which was immediately measured with an ultraviolet-visible spectrophotometer.

The air pump used in all experiments blown air with an air output of 200 mL/min.

The catalytic degradation experiment is carried out in a 250mL beaker at normal temperature and pressure, and the pollutant is tetracycline hydrochloride (TC) with the concentration of 10 mg/L. The amount of catalyst added was 2g/L and the amount of formic acid added was 46.6mmol/L, and after a certain time interval, the reaction mixture was taken out and filtered through a 0.45 μm membrane to remove the catalyst, and immediately subjected to High Performance Liquid Chromatography (HPLC) for measurement.

Performance test example 1

AR-73 is a widely used azo dye, TC is a broad-spectrum antibiotic, and is a novel degradation-resistant pollutant. Therefore, in the present study, the two pollutants were first treated, and the influence of different preparation conditions on the catalyst performance was studied.

The added catalysts are the catalysts prepared in examples 1-4 and the catalysts prepared in comparative examples 1-2, when the pollutant is AR-73, the residual concentration of the pollutant is measured after 150min by filtration, and when the pollutant is TC, the residual concentration of the pollutant is measured after 120min by filtration. As can be seen from Table 4, the preparation conditions of example 1 are optimal, and the obtained catalyst achieves a catalytic removal rate of TC of 93.2% within 120min and AR-73 of 91.9% within 150 min.

TABLE 4 catalytic removal of contaminants at different preparation ratios

Catalyst and process for preparing same	AR-73 removal Rate (%)	TC removal rate (%)
			Example 1	91.9	93.2
Example 2	-	35.8
			Example 3-		85.5
Example 4	-	92.1
			Comparative example 1	75.2	88.3
Comparative example 2	75.9	40.7

Performance test example 2

FIG. 4(a) is a graph showing the results of experiments on the ability of examples 1 to 4 and comparative examples 1 to 2 (in FIG. 4(a), Pd is omitted from the name for the sake of convenience in expressing the molar ratio of Fe to Ni) to degrade tetracycline hydrochloride at sampling intervals of 0, 15, 30, 45, 60, 90, and 120. FIG. 4(b) is a graph showing the experimental results of the degradation ability of AR-73 by the catalyst prepared in example 1. As shown in FIG. 4(b), the catalyst obtained in example 1 exhibited a catalytic removal rate of AR-73 of 93.2% at 150 min. By contrast, in the absence of formic acid (without formic acid), only 10.7% of the AR-73 was removed within 150min, demonstrating the role of formic acid as a hydrogen source for the degradation of contaminant AR-73 catalyzed by example 1. Without blowing air (without air), only 10.4% of AR-73 was removed within 150min, demonstrating the role of air as an oxygen source in the experiment. The catalyst prepared in example 1 has only weak catalytic degradation capability on AR-73 directly.

Performance test example 3

In order to evaluate the catalytic stability of the catalyst, 100mL of 200mg/L AR-73 solution is added into a 250mL conical flask, 0.2g of the catalyst prepared in the example 1 is added, the adding amount of formic acid is 46.6mmol/L, the catalyst is removed through 0.45 mu m membrane filtration after reaction for 150min, the concentration of AR-73 is immediately measured by an ultraviolet visible spectrophotometer, and after the experiment is finished, the catalyst is separated by high-speed centrifugation, and is used for the next catalytic degradation experiment after being washed by distilled water for three times. The total number of the components is recycled for 4 times.

Table 5 experimental data for contaminant degradation of example 1

The results are shown in table 4, and after 4 times of recycling, the removal rate of AR-73 by the catalyst prepared in example 1 gradually decreases from 93.2% to 85.1%, which proves that example 1 has good stability against pollutant degradation. Meanwhile, this is confirmed again in the XRD pattern of fig. 5, and fig. 5 is the XRD patterns of the catalysts before and after use, and it is known that the morphology of the catalyst before and after use is relatively stable compared with the morphology of the catalyst.

Performance test example 4

In order to further study the degradation capability of the catalyst on organic pollutants. 100mL of AR-73 solutions with different concentrations are added into a 250mL conical flask, 0.2g of the catalyst prepared in example 1 and 46.6mmol/L formic acid are added, the catalyst is removed by filtering through a 0.45-micron membrane after 240min of reaction, and the concentration of AR-73 is immediately measured by an ultraviolet-visible spectrophotometer.

Table 6 experimental data for contaminant degradation of example 1

From the research results of the above graph, it can be speculated that the catalysts all show higher activity when the degradation concentration of the catalyst is lower than AR-73 at 200mg/L, and then the treatment activity of the catalyst on pollutants is relatively inhibited along with the increase of the concentration, but when the concentration reaches 800mg/L, the removal rate can still reach 45.3%.

Performance test example 5

To verify whether hydrogen peroxide is produced, the amount of hydrogen peroxide produced was measured at the same time. The catalysts prepared in example 1 and comparative examples 1 to 3 were used for hydrogen peroxide detection. 100mL of deionized solution, 46.6mmol/L of formic acid and 2g/L of each of examples 1 and comparative examples 1 to 3 were put in a 250mL beaker and divided into four groups, and after 30 minutes of reaction, the reaction mixture was taken out and filtered through a 0.45 μm membrane to remove the catalyst, (sampling intervals were 0, 30, 60, 90, 120 and 150 minutes), and the catalyst was detected by titanium sulfate spectrophotometry. The results of the assay (as shown in FIG. 6 b) showed that the hydrogen peroxide content produced in example 1 remained the highest throughout the production, reaching 1.7mM at 150 min.

Performance test example 6

To verify the type of free radicals generated during the catalyst experiments, paramagnetic resonance measurements were performed on the reactions in which the catalysts prepared in example 1 participated, using lutidine N-oxide (DMPO) and methanol. A250 mL beaker was charged with 100mL of the deionized solution, 2g/L of the catalyst prepared in example 1 and 46.6mmol/L of formic acid were added, and after 30 minutes of reaction, the reaction mixture was taken out and filtered through a 0.45 μm membrane to remove the catalyst, and as a result, it was found that a hydroxyl radical having a peak intensity of 1:2:2:1 and a hydroxyl radical having a peak intensity of 1: 1: 1:1, characteristic peak of superoxide radical.

To study the reaction mechanism in the process and to further confirm whether the radical species generated by the process play a role in the degradation of pollutants. Three separate sets of experiments were performed, the first set being normal, the second set being 3M Isopropanol (IPA) and the third set being 1mM Benzoquinone (BQ). Wherein isopropanol can be used as a production inhibitor and benzoquinone can be used as a production inhibitor. The experimental results are shown in FIG. 6(c), where the removal rate of the first group of AR-73 was 94.1%, the removal rate of the second group of AR-73 was 37.5%, and the removal rate of the third group of AR-73 was 56.4%. The production of hydroxyl radicals and superoxide radicals was again demonstrated, and at the same time, plays an important role in degrading pollutants in the experiments.

Claims

1. A preparation method of an iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst is characterized by comprising the following steps: dissolving iron salt, nickel salt and a graphite-phase carbon nitride precursor in a solvent, removing the solvent, and calcining the obtained solid to obtain an iron-nickel doped graphite-phase carbon nitride compound; and in the presence of a reducing agent, reacting the iron-nickel doped graphite-phase carbon nitride compound with a palladium catalyst to obtain the iron-nickel-palladium co-doped graphite-phase carbon nitride composite catalyst.

2. The preparation method of the iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst according to claim 1, characterized by comprising the following steps:

(3) and dispersing the powder II and a palladium catalyst in water, performing ultrasonic treatment, stirring, dropwise adding a sodium borohydride solution, and after the reaction is finished, placing the mixture in a vacuum drying oven to be dried to obtain the iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst.

3. The preparation method of the iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst according to claim 1 or 2, wherein the iron salt and the nickel salt are respectively one or more of chloride, nitrate, phosphate and sulfate of iron and nickel.

4. The preparation method of the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst according to claim 1 or 2, wherein the graphite-phase carbon nitride precursor is selected from one or more of dicyandiamide, urea, melamine and thiourea.

5. The preparation method of the iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst according to claim 1 or 2, wherein the amount of the added iron salt and nickel salt is 0.1-0.5 mmol/g relative to the amount of the graphite phase carbon nitride precursor.

6. The preparation method of the iron, nickel and palladium co-doped graphite phase carbon nitride composite catalyst according to claim 1 or 2, wherein the molar ratio of iron to nickel in the iron salt and the nickel salt is 0.5-2: 1.

7. The preparation method of the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst according to claim 1 or 2, wherein the addition amount of the palladium chloride relative to the graphite-phase carbon nitride precursor is 0.025-0.1 mmol/g; the reducing agent is sodium borohydride, and the adding amount of the reducing agent is 5-400 times of the molar amount of palladium chloride.

8. An iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst is characterized by being prepared by the preparation method of any one of claims 1 to 7.

9. An application method of degrading organic pollutants in wastewater by using an iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst is characterized in that the composite catalyst is prepared by the preparation method of any one of claims 1 to 7, and air blowing, formic acid adding and stirring are carried out in the treatment process.

10. An application method for degrading organic pollutants in wastewater by using an iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst is characterized in that the addition amount of formic acid is 20-50 mmol/L relative to the concentration of a pollutant solution; in the wastewater, the concentration of organic pollutants is 10-800 mg/L; the usage amount of the iron, nickel and palladium co-doped graphite-phase carbon nitride composite catalyst is 1-3 g/L; the organic contamination comprises one or more of dye AR-73 and tetracycline hydrochloride.