CN110743591A

CN110743591A - Preparation method and application of doped composite catalyst

Info

Publication number: CN110743591A
Application number: CN201911001362.1A
Authority: CN
Inventors: 杨淼; 方丽娟; 周春笋; 郭玉莲; 冯彦朋; 陈科; 黄国凯
Original assignee: Wuhan University of Technology WUT
Current assignee: Wuhan University of Technology WUT
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2020-02-04

Abstract

The invention discloses a preparation method and application of a doped composite catalyst. The method is a preparation method of a non-metallic material CN/CDs and metal ion Fe (II) doped composite catalyst, and the CN/CDs are prepared firstly, then the Fe (II) is doped, and CN/CD is obtained by an immersion method₃/Fe₆A catalyst. Wherein CN/CD_xThe loading amounts of CDs synthesized by the thermal polymerization method were 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, respectively. Fe (II) is loaded on CN/CD by dipping method₃Above, it is recorded as CN/CD₃/Fe₆. Then a series of Fe (II) with different concentrations are dopedHetero in CN/CD₃Preparation of CN/CD₃/Fe_yComposite materials (y is 3, 4, 5, 6), y is FeSO₄Initial concentration of solution fe (ii). The invention also discloses CN/CD₃/Fe₆The preparation method of the catalyst comprises the steps of preparing CN, preparing CDs, and thermally polymerizing urea and citric acid to obtain CN/CD_xFinally, Fe (II) is doped in CN/CD₃And (4) finishing. The method has simple process, can realize the high-efficiency removal of the dye wastewater, is easy to regenerate, and has good industrial application prospect in the aspect of water pollution treatment.

Description

Preparation method and application of doped composite catalyst

Technical Field

The invention relates to the technical field of catalytic materials, in particular to a preparation method and application of a non-metallic material CN/CDs and metal ion Fe (II) doped composite catalyst.

Background

In recent years, the average annual average worldwide is about 4200 hundred million m³The polluted wastewater is discharged to rivers, lakes and seas. Pollute nearly 5.5 trillion m³The human body can drink fresh water, which is equivalent to about 14 percent of the total runoff of the whole world. Water pollution poses serious harm to the health of people. The Fenton reaction is one of Advanced Oxidation Processes (AOPs), which generally uses less energy than direct Oxidation and the reaction principle is to generate highly reactive free radical molecules, the most common of which is hydroxyl radical (HO.), a very reactive species with a rate constant of 10 for attacking most organic molecules⁶-10⁹Lmol^-1s^-1In the range, the Fenton oxidation method has the advantages of wide application range, strong anti-interference capability, simple operation, degradation and mineralization and the like, thereby being the most popular AOPs at present.

The traditional Fenton oxidation method is limited by the pH value range and has the defects of large iron sludge amount, and the graphite phase carbon nitride (g-C)₃N₄) Is a non-metal visible light catalytic material, and is widely applied in the fields of environmental protection, wastewater treatment and the like. Due to its physics and chemistryThe material has the advantages of stable property, environmental friendliness and low cost, can exist in acid-base solution, and is considered to be a photocatalytic material with good development prospect. Can be used for illumination production H₂、CO₂Reduction and degradation of organic contaminants. CDs, which have been found to have been developed for over a decade in 2004, have been widely used in the fields of sensors, photocatalytic water splitting and light emitting diodes, etc. due to their excellent optoelectronic properties, non-toxicity and good biocompatibility.

CDs can be H so far₂O₂The composite material synthesized by CN/CDs can be used for H without illumination₂O₂Decompose to generate HO, and calculate H₂O₂Decomposition of H under the system of/CN/CDs₂O₂Has a reaction rate constant greater than that of a series of non-metal oxides, and has a low activation energy. The composite material pair H₂O₂Has high selectivity, forms an adsorption catalysis double site by catalyzing CDs on the adsorption site, and can solve the problem of g-C₃N₄H generated in situ in the photocatalytic direction₂O₂Poisoning problems, so that higher energy conversion efficiency can be obtained.

In many researches, metal ions and nonmetal catalytic materials are coupled to improve the catalytic performance of the materials, a reaction principle different from a photocatalysis mechanism is selected, a homogeneous Fenton method and a Fenton-like method are combined under the condition of not depending on external energy input of illumination radiation or ultrasonic waves, and a novel catalytic method which is low in energy consumption, low in cost and environment-friendly is formed under the condition of additionally adding an oxidant.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: in order to overcome the defects of the technology, a preparation method and application of a non-metal material CN/CDs and metal ion Fe (II) doped composite catalyst which has low energy consumption, low cost and environmental protection are provided.

The invention adopts the following technical scheme for solving the technical problems:

the invention combines the traditional Fenton method with a non-metal catalyst, overcomes the defects of the Fenton method and the similar Fenton method, and adopts the method in H₂O₂The method is applied to the field of treating organic dye wastewater. The graphite phase carbon nitride can adsorb H in the solution₂O₂The carbon sites on the support and Fe (II) may be such that H₂O₂The composite material prepared by the principle solves the problem of H generated in situ by photocatalysis₂O₂The difficult problem of poisoning CN can be achieved, and simultaneously, higher conversion efficiency can be obtained. In addition, the insoluble composite material can generate HO under acid and alkali conditions, and can perform non-selective oxidation on the dye wastewater, thereby avoiding the problems of sludge generation and the like under pH value and alkaline conditions in the conventional oxidation technology. CN/CD prepared in addition₃/Fe₆Low material price, wide application range, strong catalytic degradation effect and the like.

The invention discloses a preparation method of a doped composite catalyst, which is a preparation method of a non-metallic material CN/CDs and a metal ion Fe (II) doped composite catalyst₃/Fe₆A catalyst.

The catalyst is prepared by taking a conjugated polymer non-metal framework material CN with a graphite structure as a carrier and CDs and Fe (II) as active components; wherein CDs are loaded on the carrier by a thermal polymerization method with citric acid as a carbon source, the loading amounts are respectively 0.5-6 wt%, and Fe (II) is doped in CN/CDs by an immersion method, the doping amounts are respectively 3-6 mM; the compound of Fe (II) is FeSO₄The solvent used in the impregnation method is water.

The invention also discloses a preparation method of the non-metallic material CN/CDs and metal ion Fe (II) doped composite catalyst, which comprises the following steps:

(1)g-C₃N₄preparing;

(2) preparing CDs;

(3)g-C₃N₄preparation of/CDs;

(4)CN/CD₃/Fe₆and (4) preparing.

The method specifically comprises the following steps:

(1)g-C₃N₄the preparation of (1):

and putting the urea into a crucible, putting the urea into a muffle furnace together for heating, naturally cooling, and taking out to obtain a light yellow solid. And then, respectively cleaning the obtained solid once by using deionized water, HCl, NaOH and deionized water to remove impurities on the surface of the solid. Finally, the obtained sample is placed in a drying box to be heated to obtain a dried solid, and the dried solid is ground to obtain light yellow powder which is recorded as CN;

(2) preparing CDs;

4g of citric acid is poured into the crucible, and then the crucible is placed into a muffle furnace to be heated to a certain temperature and kept for a period of time. Cooling to room temperature gave an orange solid noted as CDs, which was dissolved with NaOH solution and then pH adjusted to neutral with NaOH to give CDs solution.

(3) Preparation of CN/CDs:

citric acid is taken as a precursor of the carbon dots, and a similar thermal polymerization method is adopted to prepare the carbon nanodot/graphite phase carbon nitride. The method comprises the following steps: taking x as an example, citric acid and urea are uniformly mixed and put into a crucible, the crucible and the mixture are put into a muffle furnace to be heated, and then the mixture is naturally cooled and taken out to obtain a black solid. And then washing the obtained black solid with deionized water, HCl and NaOH respectively, and then washing once with the deionized water to remove impurities on the surface of the solid. Heating the obtained sample in a drying oven to obtain dried solid, grinding to obtain black powder, and recording as CN/CD₃. Preparation of a series of CN/CD with different contents_x(x ═ 1, 2, 3, 4, 5, 6), where x is the initial mass ratio of citric acid to urea;

(4)CN/CD₃/Fe₆the preparation of (1):

the preparation of the Fe (II) modified carbon nano-dot/graphite phase carbon nitride ternary composite material adopts a synthesis step of an impregnation method. The specific method is to prepare the CN/CD₃Binary composite material in FeSO₄The solution is stirred evenly. Ultrasonically dispersing the suspension, heating and stirring until the suspension is dried, and grinding the obtained sample into powderFinally, it is recorded as CN/CD₃/Fe₆. Followed by preparation of a series of Fe (II) -doped CN/CD with different concentrations₃/Fe_yTernary composites (y ═ 3, 4, 5, 6) in which y is FeSO₄Initial concentration of solution fe (ii).

Preferably, in the step (1), the precursor of CN is urea, and the synthesis is performed by a thermal polymerization method. The reaction conditions are as follows: raising the temperature to 600 ℃ at the speed of 1 ℃/min, and preserving the temperature for 3 h. Too low a temperature or too short a time may affect the product, and higher yields may be achieved under the preferred reaction conditions.

Further preferably, the concentrations of HCl and NaOH are 0.1 mol/L.

Preferably, in the step (1), after the thermal polymerization, the temperature in the muffle furnace is slowly cooled to room temperature at a cooling rate of 1 ℃/min.

In the step (2), the temperature in the muffle furnace cannot exceed 200 ℃, and the heat preservation time cannot be less than 30 min.

In the step (3), the mass ratio of the citric acid to the urea is 1:200, 1:100, 1:50, 3:100, 1:25 and 3:50 respectively.

The volume of the CN pore channel is limited, and in order to increase the specific surface area of the CN, the invention adopts a thermal polymerization method to load CDs on the surface of the CN, so that the specific surface area and the pore size of the CN can be increased, and the adsorption capacity is enhanced.

FeSO₄The aqueous solution of (A) should not be heated too fast, CN/CD₃And ferrous ion water solution is loaded into the pore canal, and the water solution and the ferrous ion water solution are well dispersed by an ultrasonic disperser. And then, ensuring that the stirring speed is not too fast or too slow, the ferrous ion aqueous solution cannot be well dispersed, the contact area is small, preferably, the stirring speed is 400r/min, the reaction temperature is 60 ℃, and the drying time is 6-7 hours.

The prepared catalyst preferably has the Fe (II) loading of 6mM, and the catalyst at the loading has the best effect on the degradation of the dye.

The invention discloses the application of the catalyst in organic dye; the using conditions of the catalyst are as follows: the temperature was 25 ℃. Preferably, the catalyst prepared by the invention is more suitable for treating organic wastewater. Especially under the condition of normal temperature, such as 25 ℃, the conversion rate of the catalyst prepared by the invention to methylene blue is as high as 100%.

After the catalyst is used, the catalyst is washed and centrifuged by using a volatile solvent, a product and an intermediate product attached to the catalyst are washed off, and then the catalyst is heated to 50-80 ℃ in a vacuum state and kept for 5-6 hours to realize regeneration.

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

1. the traditional Fenton method has very high requirements on pH, can generate iron sludge and cannot be popularized in a large range. Therefore, the invention combines the traditional Fenton method with a non-metal catalyst, overcomes the defects of the traditional Fenton method, and adopts the method in H₂O₂The method is applied to the field of treating organic dye wastewater.

2. The graphite phase carbon nitride can adsorb H in the solution₂O₂The carbon sites on the support and Fe (II) may be such that H₂O₂The composite material prepared by the principle solves the problem of H generated in situ by photocatalysis₂O₂The difficult problem of poisoning CN can be achieved, and simultaneously, higher conversion efficiency can be obtained.

3. The insoluble composite material can generate HO & lt- & gt under acid-base conditions, and can perform non-selective oxidation on the dye wastewater, thereby avoiding the problems of sludge generation and the like under the conditions of pH value and alkalinity of the conventional oxidation technology. CN/CD prepared in addition₃/Fe₆Low material price, wide application range, strong catalytic degradation effect and the like.

CN/CD prepared by the invention₃/Fe₆The catalyst has strong catalytic action on organic dye wastewater, and can show 100% conversion rate at lower temperature. Compare CN/CD₃The degradation rate of the dye is greatly improved.

Description of the drawings:

FIG. 1 shows CN, CN/CD prepared in examples 1, 2 and 4₃And CN/CD₃/Fe₆Infrared profiles of the three materials;

FIG. 2 shows CN, CN/CD prepared in examples 1 and 4₃/Fe₆Transmission electron microscopy images of (a). In FIG. 2, A is a transmission electron micrograph of CN, B is a transmission electron micrograph of CN, and C is CN/CD₃/Fe₆D is CN/CD₃/Fe₆E is CN/CD₃/Fe₆F is CN/CD₃/Fe₆Transmission electron microscopy images of (a).

FIG. 3 shows CN, CN/CD prepared in examples 1, 2 and 4₃And CN/CD₃/Fe₆Adsorption isotherms of the three materials;

FIG. 4 shows CN, CDs and CN/CD prepared in examples 1, 2, 3 and 4₃/Fe₆And CN/CD with different loading amounts_xXRD characterization pattern of (a).

Detailed Description

The invention discloses a non-metal material CN/CDs and Fe (II) doped composite catalyst, which combines the traditional Fenton method and the non-metal catalyst to overcome the defects of the traditional Fenton method and synthesizes CN/CD by a thermal polymerization method_xThe loading amounts of CDs were 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, respectively. Fe (II) is loaded on CN/CD by dipping method₃Above, it is recorded as CN/CD₃/Fe₆. Then a series of Fe (II) with different concentrations are doped in CN/CD₃Preparation of CN/CD₃/Fe_yComposite materials (y ═ 3, 4, 5, 6), where y is FeSO₄Initial concentration of solution fe (ii).

The invention also discloses the CN/CD₃/Fe₆The preparation method of the catalyst comprises the following steps: firstly preparing CN, then preparing CDs, then thermal polymerizing urea and citric acid to obtain CN/CD_xFinally, Fe (II) is doped in CN/CD₃Obtaining the catalyst CN/CD₃/Fe_y. The catalyst has simple preparation process and mild condition, can realize the high-efficiency removal of the dye wastewater, is easy to regenerate, and has good industrial application in the aspect of water pollution treatmentAnd (4) foreground.

The following examples further illustrate the invention, but the content of the invention is not limited thereto at all.

Example 1

(1)g-C₃N₄The preparation of (1):

g-C₃N₄the preparation method comprises the following steps of weighing 50g of urea, putting the urea into a crucible, putting the urea into a muffle furnace together, heating to 600 ℃ at the speed of 1 ℃/min, preserving heat for 3h, naturally cooling, and taking out to obtain a light yellow solid. And then sequentially washing the obtained solid with deionized water, 0.1mol/L HCl, 0.1mol/L NaOH and deionized water once respectively to remove impurities on the surface of the solid. And finally, putting the obtained sample in a drying oven to be heated for 2 hours at the heating temperature of 100 ℃ to obtain a dried solid, and manually grinding the dried solid to obtain light yellow powder which is recorded as CN.

(2) Preparing CDs;

pouring 4g of citric acid into a crucible, then putting the crucible into a muffle furnace to heat to 200 ℃, wherein the heating rate is 5 ℃/min, and keeping the temperature for 40 min. Cooling to room temperature gave an orange solid noted CDs, which was dissolved in 10g/L NaOH solution and then adjusted to neutral pH with NaOH to give a CDs solution.

(3) Preparation of CN/CDs:

citric acid is taken as a precursor of the carbon dots, and a similar thermal polymerization method is adopted to prepare the carbon nanodot/graphite phase carbon nitride. The specific method comprises the steps of uniformly mixing 1.5g of citric acid and 50g of urea, putting the mixture into a crucible, putting the crucible and the mixture into a muffle furnace, heating to 600 ℃ at the speed of 1 ℃/min, preserving the temperature for 3 hours, naturally cooling, and taking out to obtain a black solid. And then sequentially washing the obtained solid with deionized water, 0.1mol/L HCl, 0.1mol/L NaOH and deionized water once respectively to remove impurities on the surface of the solid. Finally, the obtained sample is placed in a drying oven to be heated for 2 hours at the heating temperature of 100 ℃ to obtain a dried solid, and the dried solid is manually ground to obtain black powder, namely CN/CD with the load of 3wt percent₃。

(4)CN/CD₃/Fe₄The preparation of (1):

the preparation of the Fe (II) modified carbon nano-dot/graphite phase carbon nitride ternary composite material adopts a synthesis step of an impregnation method. The specific method is to prepare the CN/CD₃Weighing 0.4g of binary composite material, and adding into 100mL of 4mM FeSO₄The solution is stirred evenly. Ultrasonically dispersing the suspension for 25min, heating and stirring at 60 deg.C until drying, manually grinding the obtained sample into powder to obtain CN/CD with 4mM loading₃/Fe₄。

The degradation rate of the catalyst prepared by the embodiment to methylene blue can reach 100% under atmospheric pressure by using an ultraviolet-visible spectrophotometer method for testing.

Example 2

(1)CN/CD₃The load of (2):

taking 50g of urea and 1.5g of citric acid, uniformly mixing, putting into a crucible, putting into a muffle furnace together, heating to 600 ℃ at the speed of 1 ℃/min, preserving heat for 3h, naturally cooling, and taking out to obtain a black solid. And then sequentially washing the obtained solid with deionized water, 0.1mol/L HCl, 0.1mol/L NaOH and deionized water once respectively to remove impurities on the surface of the solid. Finally, the obtained sample is placed in a drying oven to be heated at the temperature of 100 ℃ for 2 hours to obtain a dried solid, and the dried solid is manually ground to obtain black powder, namely CN/CD with the load of 3 wt%₃。

(2)CN/CD₃/Fe₅The load of (2):

the obtained CN/CD₃0.4g of the suspension was weighed into a container and 100ml of 5mM FeSO was added₄Ultrasonically dispersing the solution for 25min, heating and stirring at 60 deg.C until drying, manually grinding the obtained sample into powder to obtain CN/CD with a loading of 5mM₃/Fe₅。

The conversion of methylene blue by the catalyst prepared in this example was 100% at atmospheric pressure as measured by uv-vis spectrophotometer.

Example 3

(1)CN/CD₃The load of (2):

(2)CN/CD₃/Fe₆The load of (2):

the obtained CN/CD₃0.4g of the suspension was weighed into a container, and 100ml of 6mM FeSO was added₄Performing ultrasonic dispersion on the solution for 25min, heating and stirring at 60 ℃ until the solution is dried, manually grinding the obtained sample, and grinding into powder to obtain CN/CD with the load of 6mM₃/Fe₆。

Application example 1 Water pollution treatment

The average annual worldwide is about 4200 hundred million m³The polluted wastewater is discharged to rivers, lakes and seas. Pollute nearly 5.5 trillion m³The amount of the potable fresh water is about 14 percent of the total amount of the global runoff. Water pollution poses serious harm to the health of people.

CN/CD prepared by the invention₃/Fe₆The catalyst can be used for catalyzing and decomposing pollutants in water such as dye wastewater, medicines and personal care products, and the conversion rate can reach 100%.

Application example 2 photocatalytic hydrogen production

At present, the world energy is in short supply, and hydrogen is used as a novel clean energy, so that the emission can be reduced, the dependence on fossil energy is reduced, and great research significance is realized.

CN/CD prepared by the invention₃/Fe₆The catalyst can be inCatalytic decomposition of H in the field of photocatalysis₂O produces hydrogen.

Claims

1. A process for preparing the doped composite catalyst includes such steps as preparing CN/CDs, doping Fe (II), and immersing to obtain said CN/CD₃/Fe₆A catalyst.

2. The preparation method of the doped composite catalyst according to claim 1, wherein the catalyst is prepared by taking a conjugated polymer non-metal framework material CN with a graphite structure as a carrier and CDs and Fe (II) as active components; wherein CDs are loaded on the carrier by a thermal polymerization method with citric acid as a carbon source, the loading amounts are respectively 0.5-6 wt%, and Fe (II) is doped in CN/CDs by an immersion method, the doping amounts are respectively 3-6 mM; the compound of Fe (II) is FeSO₄The solvent used in the impregnation method is water.

3. The preparation method of the doped composite catalyst according to claim 2, wherein the urea is put into a crucible, put into a muffle furnace together for heating, then naturally cooled, and taken out to obtain a light yellow solid; then, sequentially washing the obtained solid by using deionized water, HCl, NaOH and deionized water once respectively to remove impurities on the surface of the solid; finally, the obtained sample is placed in a drying oven to be heated to obtain a dried solid, and the dried solid is ground to obtain light yellow powder g-C₃N₄And is referred to as CN.

4. The method for preparing the doped composite catalyst according to claim 3, wherein the amount of the urea is 50g, the concentrations of HCl and NaOH are 0.1mol/L, and the heating reaction conditions are as follows: raising the temperature to 600 ℃ at the speed of 1 ℃/min, and preserving the temperature for 3 h.

5. The method of claim 2, wherein the CDs are prepared by the following method; pouring 4g of citric acid into a crucible, then placing the crucible into a muffle furnace, heating the crucible to a certain temperature, keeping the temperature for a period of time, then cooling the crucible to room temperature to obtain orange solids, recording the orange solids as CDs, dissolving the solid CDs by using a NaOH solution, and finally adjusting the pH value to be neutral by using NaOH to obtain a CDs solution.

6. The method for preparing the doped composite catalyst of claim 5, wherein the concentration of NaOH is 10g/L, and the heating reaction conditions are as follows: raising the temperature to 200 ℃ at the speed of 5 ℃/min, and preserving the temperature for 40 min.

7. The method of claim 2, wherein CN/CDs is prepared by the following method;

the preparation method of the carbon nanodot/graphite phase carbon nitride by using citric acid as a precursor of the carbon dots and adopting a thermal polymerization method comprises the following steps: taking x as an example, uniformly mixing citric acid and urea, putting the mixture into a crucible, putting the crucible and the mixture into a muffle furnace, heating, naturally cooling, and taking out to obtain a black solid; then, sequentially washing the obtained solid by using deionized water, HCl, NaOH and deionized water once respectively to remove impurities on the surface of the solid; heating the obtained sample in a drying oven to obtain dried solid, and grinding to obtain black powder which is binary composite material CN/CD₃；

Finally, a series of CN/CD with different contents are prepared by a thermal polymerization method_xAnd x is 1, 2, 3, 4, 5 and 6, and x is the initial mass ratio of the citric acid to the urea.

8. The method for preparing the doped composite catalyst of claim 7, wherein the amount of urea is 50g, the amount of citric acid is 1.5g, the concentrations of HCl and NaOH are 0.1mol/L, and the heating reaction conditions are as follows: raising the temperature to 600 ℃ at the speed of 1 ℃/min, and preserving the temperature for 3 h.

9. The method for preparing the doped composite catalyst according to claim 2, wherein the CN/CD is synthesized by the following impregnation method₃/Fe₆: the CN/CD prepared by the method of claim 7₃In FeSO₄Uniformly stirring the solution, and grinding a sample obtained after ultrasonic dispersion and heating and stirring for 6-7 hours till the sample is dried into powder which is CN/CD₃/Fe₆(ii) a Followed by preparation of a series of Fe (II) -doped CN/CD with different concentrations₃/Fe_yTernary composite materials, y being 3, 4, 5, 6, where y is FeSO₄Initial concentration of solution fe (ii).

10. The method of claim 9, wherein the CN/CD is a CD catalyst₃0.4g, FeSO₄The solution is 100mL of 6mM, and the reaction conditions are as follows: the suspension is ultrasonically dispersed for 25min and heated and stirred at 60 ℃.