CN111715261A - Application of G-C3N4 catalyst in degradation of organic dyes in high-salt wastewater - Google Patents

Abstract

The invention relates to the technical field of photocatalysis, and particularly discloses G-C₃N₄The application of the catalyst in degrading organic dye in high-salinity wastewater has the advantages of simple process, low cost and environmental protection, and the catalyst can efficiently remove the organic dye in water under a wide range of sodium chloride concentration and reduce environmental pollution.

Description

Application of G-C3N4 catalyst in degradation of organic dyes in high-salt wastewater

technical field

The invention relates to the technical field of photocatalysis, and specifically discloses the application of a GC ₃ N ₄ catalyst in degrading organic dyes in high-salt wastewater.

Background technique

The rapid development of industry has greatly promoted the progress of human civilization, but also caused a series of environmental problems, such as organic pollutants in high-salt organic wastewater, which seriously threatens human health. Most of the organic pollutants in high-salt organic wastewater come from seawater used in production and living processes, industrial production and many other fields, and the amount of water is increasing year by year. The direct discharge of organic pollutants in high-salt organic wastewater into soil and water will cause serious problems. of destruction. Therefore, the treatment of organic pollutants in high-salt organic wastewater has become one of the key and hot issues in the field of environmental protection research. There are many ways to treat organic pollutants in high-salt organic wastewater, but there are also many problems. For example, using Fenton or Fenton-like technology to remove organic dyes under high-salt conditions is prone to produce more toxic halogen salts. Therefore, timely research and development of methods for removing organic dyes in high-salt wastewater has important practical significance and economic value for solving the environmental pollution problems caused by it and recovering salts.

Photocatalytic oxidation technology has the advantages of mild reaction conditions, complete mineralization, and environmental protection, and has been favored by researchers for a long time. So far, photocatalytic technology has been used to treat organic pollutants in high-salt wastewater, and the photocatalysts used are mainly metal-based catalysts. For example, Chinese patent (201910510947.X) discloses a composite photocatalyst for the treatment of rose Bengal B in high-salt wastewater The preparation method and application thereof, wherein, the composite photocatalyst is composed of silver phosphate, polyaniline and chromium-doped strontium titanate; Chinese patent (201711046176.0) discloses porous graphite phase nitrogen-supported bismuth oxycarbonate as a photocatalyst to treat high-salt wastewater Medium organic dyes. However, metal-based catalysts have the problem of secondary pollution; and because chloride ions in high-salt solutions are adsorbed on the surface of metal-based catalysts to form chlorine radical species, chlorine radical species can combine with reactants to form highly toxic hypochlorite acid salt. In addition, chlorine radical species can combine with photogenerated electrons to generate chloride ions, which consumes part of the photogenerated hole-electron pairs and affects the photocatalytic performance of metal-based catalysts. Compared with metal-based photocatalysts, non-metal-based photocatalysts are more attractive to degrade organic pollutants in water under high-salt conditions. Literature (Appl.Catal.B:Environ.2014, 158-159:321-328) reported graphitic nitrogen carbide (molecular formula: gC ₃ ) under the condition of different sodium salts (Na ₂ SO ₃ , NaCl and Na ₂ SO ₄ ). N ₄ ) visible light degradation of organic dyes, the results show that these sodium salts can promote the degradation of organic dyes in water under visible light, but the reaction rate is slow. In addition, it is worth exploring whether the catalyst can withstand the influence of higher sodium chloride concentration for wider industrial application. The literature (Chem.Eng.J.2012,192:171-178) has studied the effect of chloride ion concentration on the photocatalytic degradation of organic dye AO7 by _TiO2 . The study shows that when the chloride ion concentration is lower than 200mM, the chloride ion can enhance the The performance of the photocatalyst; when the chloride ion concentration is higher than 200mM, the chloride ion plays a significant inhibitory role on the photocatalyst. It can be seen that the level of sodium chloride concentration is an important factor restricting the development of this technology. In a word, the photocatalyst used in the prior art degrades organic dyes in water under the condition of sodium chloride, which has the disadvantages of easily causing secondary pollution, slow reaction rate, and low concentration of sodium chloride. Therefore, it is necessary to develop a new method for efficient degradation of organic dyes in high-salt wastewater.

SUMMARY OF THE INVENTION

In view of this, the present invention provides an application of a GC ₃ N ₄ catalyst in degrading organic dyes in high-salt wastewater, and using the catalyst to degrade organic dyes in high-salt wastewater has the advantages of simple use, low cost and environmental protection, and can be used. It can efficiently remove organic dyes in water under a wide range of sodium chloride concentrations, reducing environmental pollution.

The application of the GC ₃ N ₄ catalyst provided by the present invention in degrading organic dyes in high-salt wastewater, the GC ₃ N ₄ catalyst is a porous nano-sheet structure catalyst prepared by the following method:

The gC ₃ N ₄ precursor was calcined at 550-600 ° C for 2-4 h to obtain gC ₃ N ₄ solid; then the gC ₃ N ₄ solid was hydrothermally treated at 160-200 ° C for 2-8 h, rinsed, dried, and ground gC ₃ N ₄ powder is formed; finally, the gC ₃ N ₄ powder is placed in a covered crucible, calcined at 500-550° C. for 2-8 hours, and rapidly cooled to obtain the GC ₃ N ₄ catalyst.

Preferably, the mass ratio of the gC ₃ N ₄ powder to the volume of the crucible is 0.10-0.14 g:50 mL.

Preferably, the gC ₃ N ₄ precursor is melamine.

Preferably, the specific process of using the GC ₃ N ₄ catalyst to degrade organic dyes in high-salt wastewater is as follows: adding the GC ₃ N ₄ catalyst to the high-salt wastewater containing organic dyes, stirring vigorously under dark conditions, After equilibration for 30 min, degradation treatment was carried out under light conditions.

More preferably, the added amount of the GC ₃ N ₄ catalyst is 0.1-1.0 g/L.

More preferably, the organic dye is one of Rhodamine B, methylene blue and methyl orange.

More preferably, the illumination is one of LED, Xe lamp and sunlight.

Compared with the prior art, the present invention has the following beneficial technical effects:

1. Efficiently remove organic dyes in wastewater under a wide range of sodium chloride concentrations, and there is no obvious inhibitory effect;

2. There will be no secondary pollution during the entire wastewater treatment process;

3. The used catalyst has the characteristics of simple preparation, green environmental protection and low cost, and the catalyst is easy to recover and can be reused.

Description of drawings

Fig. 1 is the scanning electron microscope (SEM) image of the catalyst provided by Example 1 and Comparative Example 1, wherein, Fig. a is the electron microscope image of gC ₃ N ₄ , and Fig. b is the electron microscope image of GC ₃ N ₄ ;

Fig. 2 is the removal rate figure of RhB in the organic dye processing method that embodiment 1 and comparative example 1 provide;

Fig. 3 is the removal rate figure of RhB under the different sodium chloride concentrations that embodiment 4 provides;

4 is a diagram showing the removal rate of RhB under different dosages of the catalyst provided in Example 5.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only for the present invention and are not intended to limit the scope of the present invention.

The application of the GC ₃ N ₄ catalyst provided by the present invention in degrading organic dyes in high-salt wastewater, the GC ₃ N ₄ catalyst is a porous nano-sheet structure catalyst prepared by the following method;

The gC ₃ N ₄ precursor was calcined at 550-600 ° C for 2-4 h to obtain gC ₃ N ₄ solid; then the gC ₃ N ₄ solid was hydrothermally treated at 160-200 ° C for 2-8 h, rinsed, dried, and ground gC ₃ N ₄ powder is formed; finally, the gC ₃ N ₄ powder is placed in a covered crucible, calcined at 500-550° C. for 2-8 hours, and rapidly cooled to obtain the GC ₃ N ₄ catalyst.

The following description will be given in conjunction with specific embodiments.

Example 1

At room temperature, prepare 50 mL of a mixed solution containing 10 mg/L Rhodamine B (labeled as RhB) and 500 mM NaCl, put it into a photocatalytic reactor, add 1.0 g/L GC ₃ N ₄ , and stir vigorously in the dark 30min, the purpose is that the reactants can reach the adsorption-desorption equilibrium on the catalyst surface under the condition of dark light; then the photocatalytic reaction is carried out under the LED radiation, the reaction solution is taken out at regular intervals, separated, measured its absorbance, and calculated RhB degradation Rate;

Wherein, the preparation process of GC ₃ N ₄ is:

Put the precursor melamine into the covered crucible, roast the melamine at 550°C for 4 hours to obtain a light yellow gC ₃ N ₄ solid, which is ground for use, and the crucible is covered to prevent the melamine from volatilizing due to sublimation; weigh 0.3 g of the ground The gC ₃ N ₄ powder was placed in a 50 mL crystallization kettle, 25 mL of high-purity water was added, hydrothermally treated at 180 °C for 4 h, rinsed, dried, and ground to obtain the sample powder; in a 50 mL covered crucible, 0.10 g of the sample powder was added, and the sample powder was heated at 550 After calcining again at ℃ for 4h, the desired catalyst is obtained, which is marked as GC ₃ N ₄ .

In the above preparation process of GC ₃ N ₄ , the sample after hydrothermal treatment is ground into sample powder, which can fully contact the sample under high temperature calcination with air. The purpose of the covered roasting is to prevent the sample from burning out completely. The ratio of sample mass to crucible volume has strict requirements. This is because in a crucible of a certain volume, the amount of the sample to be heated is too much, and it is difficult to obtain the desired target catalyst, while the amount of the sample to be heated is too small, and there is no sample. residue.

Preparation principle: calcining melamine at high temperature to obtain gC ₃ N ₄ nanosheets, continue to perform hydrothermal treatment on gC ₃ N ₄ nanosheets, and partially exfoliate the gC ₃ N4 nanosheets; the second high temperature calcination can exfoliate the partially exfoliated gC 3 N ₄ nanosheets. ₃ N ₄ was further exfoliated. At the same time, part of the _gC3N4 nanosheets _were decomposed into gas, and a large number of pores _were formed through the _{gC3N4 nanosheets} , so that the _gC3N4 presented a porous nanosheet structure. The electron microscope image of the prepared GC ₃ N ₄ catalyst is shown in Figure 1, Figure 1 (a) is the electron microscope image of gC ₃ N ₄ provided by Comparative Example 1, and Figure 1 (b) is the GC ₃ N ₄ provided by Example 1. Electron micrograph. _gC3N4 is composed _of particles aggregated by _nanosheets , and _GC3N4 exhibits a porous nanosheet structure. It can be seen from Fig. 1 that the structure of the finally prepared catalyst changed greatly compared with the control catalyst.

Figure 2 shows the degradation results of RhB after mixing the mixed solution of RhB and NaCl with the GC ₃ N ₄ catalyst. It can be seen from Figure 2 that RhB was completely degraded within 30 min.

The principle of photodegradation reaction: under the action of light excitation, photogenerated hole-electron pairs are generated on the surface of the catalyst. Among them, the photogenerated holes are oxidative and can be directly used to oxidize organic dyes. In addition, photogenerated electrons can combine with dissolved oxygen in water to generate peroxy radical species, which can also degrade organic dyes. In the presence of NaCl, Na ⁺ is adsorbed on the catalyst surface and Cl ^- is in the reaction solution, so that the photogenerated holes do not combine with Cl ^- to form Cl species, which will not form more toxic hypochlorite acid salt.

Example 2

The only difference from Example 1 is:

During the preparation of GC ₃ N ₄ , 0.12 g of the hydrothermally treated sample powder was added, and calcined again at 550° C. for 4 h to prepare a GC ₃ N ₄ catalyst.

The GC ₃ N ₄ catalyst was photocatalytically reacted with 50 mL of a mixed solution containing 10 mg/L RhB and 500 mM NaCl for 30 min, and the RhB degradation rate reached 99%.

Example 3

The only difference from the above-mentioned embodiment is:

During the preparation of GC ₃ N ₄ , 0.14 g of the hydrothermally treated sample powder was added and calcined again at 550° C. for 4 h to prepare a GC ₃ N ₄ catalyst.

The GC ₃ N ₄ catalyst was photocatalytically reacted with 50 mL of a mixed solution containing 10 mg/L RhB and 500 mM NaCl for 30 min, and the RhB degradation rate reached 99%.

Example 4

Photodegradation of RhB in high-salt wastewater under different concentrations of sodium chloride

At room temperature, prepare 50 mL of a mixed solution containing 10 mg/L RhB and NaCl, wherein the NaCl concentrations are 1 mM, 10 mM, 100 mM, 300 mM and 500 mM, respectively, put into the photocatalytic reactor, and add 1.0 g/L GC ₃ N ₄ (the preparation method is the same as the preparation method of GC ₃ N ₄ in Example 1), stir vigorously for 30min under dark conditions; then carry out photocatalytic reaction under LED radiation, take out the reaction solution at intervals, separate, measure its absorbance, The RhB degradation rate was calculated and the results are shown in Figure 3.

It can be seen from Figure 3 that RhB was completely degraded within 30 min.

Example 5

Photodegradation of RhB in high-salt wastewater under different catalyst dosages

At room temperature, prepare 50 mL of a mixed solution containing 10 mg/L RhB and 500 mM NaCl, put it into a photocatalytic reactor, and add a GC ₃ N ₄ catalyst (the preparation method is the same as the preparation method of GC ₃ N ₄ in Example 1), Among them, the dosage of GC ₃ N ₄ catalyst was 0.1 g/L, 0.3 g/L, 0.5 g/L, 0.7 g/L and 1.0 g/L, respectively, and vigorously stirred for 30 min under dark conditions; then under LED radiation The photocatalytic reaction was carried out, the reaction solution was taken out at regular intervals, separated, its absorbance was measured, and the RhB degradation rate was calculated. The results are shown in Figure 4.

As can be seen from Figure 4, RhB was completely degraded within 30 min.

Comparative Example 1

The only difference from Examples 1-3 is:

The preparation process of the catalyst is as follows:

The precursor melamine was added to the covered crucible, and the melamine was calcined at 550° C. for 4 h to obtain a light yellow gC ₃ N ₄ solid, which was ground for use.

The light yellow gC ₃ N ₄ solid was photocatalytically reacted with 50 mL of a mixed solution containing 10 mg/L RhB and 500 mM NaCl for 30 min. The results are shown in FIG. 2 .

It can be seen from Figure 2 that the degradation rate of RhB on gC ₃ N ₄ is only 30% within 30 min.

Compared with gC ₃ N ₄ , the catalytic activity of GC ₃ N ₄ is significantly improved, mainly due to the large changes in its structure, such as the large changes in morphology, as shown in Figure 1. The change of morphology leads to a substantial increase in the specific surface area of the material, which in turn affects its ability to adsorb RhB.

It should be noted that when the claims of the present invention relate to the numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected, because the steps and methods used are the same as the examples, To avoid repetition, the present invention describes preferred embodiments, but those skilled in the art may make additional changes and modifications to these embodiments once the basic inventive concepts are known. Therefore, the appended claims are intended to be construed to include the preferred embodiment and all changes and modifications that fall within the scope of the present invention.

Those skilled in the art should understand that the above descriptions are only several specific embodiments of the present invention, and the present invention is not limited thereto. It should be pointed out that for those of ordinary skill in the art, many modifications and improvements can also be made, and all modifications or improvements that do not exceed the claims should be regarded as the protection scope of the present invention.

Claims (7)

1. Application of a GC ₃ N ₄ catalyst in degrading organic dyes in high-salt wastewater, the GC ₃ N ₄ catalyst is a porous nanosheet structure catalyst prepared by the following method; The gC ₃ N ₄ precursor was calcined at 550-600 ° C for 2-4 h to obtain gC ₃ N ₄ solid; then the gC ₃ N ₄ solid was hydrothermally treated at 160-200 ° C for 2-8 h, rinsed, dried, and ground gC ₃ N ₄ powder is formed; finally, the gC ₃ N ₄ powder is placed in a covered crucible, calcined at 500-550° C. for 2-8 hours, and rapidly cooled to obtain the GC ₃ N ₄ catalyst. 2 . The application according to claim 1 , wherein the mass ratio of the gC ₃ N ₄ powder to the volume of the crucible is 0.10-0.14 g: 50 mL. 3 . 3. The application according to claim ₁ , wherein the _gC3N4 precursor is melamine. 4. application according to claim 1 is characterized in that, the concrete process that adopts described GC ₃ N ₄ catalyst to degrade organic dyes in high-salt waste water is as follows: described GC ₃ N ₄ catalyst is added to containing organic dyestuffs In the high-salt wastewater, vigorously stirred under dark conditions, equilibrated for 30 min, and then degraded under light conditions. 5 . The application according to claim 4 , wherein the GC ₃ N ₄ catalyst is added in an amount of 0.1-1.0 g/L. 6 . 6. application according to claim 4, is characterized in that, described organic dye is a kind of in Rhodamine B, methylene blue, methyl orange. 7. The application according to claim 4, wherein the illumination is one of LED, Xe lamp, and sunlight.

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