CN111939963A

CN111939963A - Preparation method of bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of photocatalyst degradation

Info

Publication number: CN111939963A
Application number: CN202010940554.5A
Authority: CN
Inventors: 姜建辉; 张国双; 颜菀旻; 崔天伊; 冯婷
Original assignee: Tarim University
Current assignee: Tarim University
Priority date: 2020-09-09
Filing date: 2020-09-09
Publication date: 2020-11-17
Anticipated expiration: 2040-09-09
Also published as: CN111939963B

Abstract

The invention discloses a preparation method of a bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of photocatalytic degradation, wherein a mixture of melamine and/or urea and a mixture of samarium salt and bismuth salt are mixed and dissolved in deionized water under magnetic stirring at room temperature; raising the temperature, stirring and heating until all water is evaporated to dryness; drying in an oven, cooling, and grinding into powder; placing the powdery sample in a tubular vacuum furnace, calcining at high temperature, cooling and grinding into powder to obtain g-C co-doped with the bimetallic elements of samarium and bismuth₃N₄Synthesizing the composite photocatalyst material. Bimetallic co-doping in the unchanged g-C₃N₄The structure increases the specific surface area of the catalyst, inhibits the recombination of photo-generated charge carriers, and improves the g-C of the catalyst₃N₄-visible light utilisation ability of Sm-Bi; g-C₃N₄The degradation rate of-Sm-Bi to MB is as high as 90.34 percent, and the-Sm-Bi is pure g-C₃N₄1.5 times of the total weight of the powder.

Description

Preparation method of bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of photocatalyst degradation

Technical Field

The invention relates to the technical field of preparation of photocatalytic materials. In particular to a preparation method of a bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of photocatalytic degradation.

Background

Since the development of the society and economy, the industrial science and technology are promoted dramatically under the background of the era of soaring development, but at the same time, the double-edged sword also causes a series of serious ecological environment threats including energy failure, dye wastewater pollution, atmospheric ozone layer holes and the like. China is a country with strong dye manufacturing and consumption, and a large amount of waste dye residues in the printing and dyeing industry cause wide pollution of water bodies, thus posing serious threat to human health. Therefore, how to solve the problem of dye pollution efficiently and without pollution has been gradually developed as an important research content in the current environmental protection category.

Among a wide variety of dye degradation technologies, the photocatalytic technology is emerging due to its strong ability to catalyze and degrade pollutants, little side effect on the environment, and the like, and in recent years, a new organic polymer semiconductor, namely graphite-like phase carbon nitride (g-C)₃N₄) It is considered as a novel visible light photocatalyst. The graphite phase carbon nitride has the outstanding advantages of simple preparation process, sheet structure similar to that of graphite and matched conduction band valence band position (g-C)₃N₄2.7eV) and stable chemical and physical properties, which has been rapidly developed as a focus in the research field of non-metal photocatalyst degradation of organic pollutants.

But original g-C₃N₄The bottle neck exists, such as the existence of the photo-generated electron-hole pair with the specific surface area being too low and the energy band gap being wider and only absorbing ultraviolet and visible lightRapid recombination, unsatisfactory photocatalytic degradation effect, low cyclic utilization rate and the like. Based on this, experts have explored various methods to improve g-C₃N₄The photocatalytic degradation effect is summarized and summarized into the following three aspects: (ii) widening of g-C₃N₄The exposed specific surface area between the sheets; ② adopting doping modification mode to reduce g-C₃N₄Band gap width of (1), extension g-C₃N₄A response range to visible light; construction of various semiconductors and g-C₃N₄A heterojunction composite photocatalyst. In particular for g-C₃N₄The modification measures include five modes including non-metal element doping, noble metal element deposition or non-noble metal element doping, dye sensitization, single-layer stripping, semiconductor material compounding and the like. Wherein metal doping is the easiest and excellent one capable of improving g-C₃N₄Means for modifying the photocatalytic activity. However, most of the studies on the modification of carbon nitride so far mainly comprise doping of single noble metal, non-noble metal or noble metal, such as Lepeng and the like with metal doped g-C₃N₄Theoretical research, Puhui Deng and the like carried out non-noble metal Ni doping g-C₃N₄Research on the catalyst, optimization of g-C by Ag doping₃N₄However, there still exist many works such as co-doping of bimetal, rare earth metal, co-doping of rare earth metal and non-noble metal, and the like, and no intensive research is carried out.

Disclosure of Invention

Therefore, the technical problem to be solved by the invention is to provide a preparation method and application of photocatalytic degradation of a bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material, which can obviously reduce the combination efficiency of a photoproduction electron hole pair and broaden the narrow absorption range of the photoproduction electron hole pair in a visible light irradiation area, and the degradation performance of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material on organic dyes in sewage is greatly improved.

In order to solve the technical problems, the invention provides the following technical scheme:

the preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material comprises the following steps:

(1) mixing a mixture of melamine and/or urea with a mixture of soluble samarium salt and soluble bismuth salt, and then dissolving the mixture in deionized water under magnetic stirring at room temperature;

(2) raising the temperature, stirring and heating until all water is evaporated to dryness, and integrally presenting a solidified state;

(3) then drying in an oven, cooling and grinding into powder;

(4) placing the powdery sample in a tubular vacuum furnace, calcining at high temperature, cooling and grinding into powder to obtain g-C co-doped with the bimetallic elements of samarium and bismuth₃N₄Synthesizing the composite photocatalyst material.

The preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material comprises the following steps of (1): the mass sum of melamine and/or urea is 10g, and the mass ratio of melamine to urea is 10:0, 8:2, 6:4, 5:5, 4:6, 2:8 and 0: 10.

According to the preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material, the soluble samarium salt is samarium nitrate, and the soluble bismuth salt is bismuth nitrate.

According to the preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material, the mass ratio of samarium nitrate to bismuth nitrate is 0.4: (0.1-1.0).

The preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material comprises the following steps of (1): the mixture of melamine and/or urea and the mixture of soluble samarium salt and soluble bismuth salt are dissolved in a beaker filled with 60mL of deionized distilled water, and then the beaker is placed on a constant-temperature magnetic electric stirrer to stir at room temperature for 30min, and all the components are fully and uniformly mixed.

In the step (2), the temperature of the constant-temperature heating magnetic stirrer is adjusted to 80 ℃, the constant-temperature stirring is carried out until all water is evaporated to dryness, and the whole composite photocatalyst material is in a solidified state.

In the step (3), the beaker in the step (2) is placed in an oven with the temperature adjusted to be 100 ℃ for drying, and after 4 hours, the sample dried into blocks is taken out and ground into powder by using an agate mortar.

In the preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material, in the step (4), the calcination parameters of the tubular vacuum furnace are as follows: the calcining temperature is 550 ℃, the heating rate is 5 ℃/min, and the constant-temperature calcining time is 4 h; cooling to below 100 ℃ after the vacuum tube furnace is calcined, taking out the sample and grinding the sample into powder to obtain g-C co-doped with the bimetallic elements of samarium and bismuth₃N₄Synthesizing the composite photocatalyst material.

The bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material prepared by the method can be used for photocatalytic degradation of methylene blue under a photocatalytic condition.

The technical scheme of the invention achieves the following beneficial technical effects:

1. the bimetal Sm-Bi co-doped g-C is prepared by adopting a one-step high-temperature calcination method₃N₄The structure and the morphology of the prepared sample are analyzed by using characterization means such as XRD, FT-IR and the like.

2. Co-doping of bimetallic in unaltered g-C₃N₄The structure effectively reduces the forbidden bandwidth of carbon nitride, increases the specific surface area of the catalyst by reducing the limitation of the catalyst on the response of visible light, inhibits the recombination of photo-generated charge carriers, and further promotes the g-C of the catalyst₃N₄The ability of Sm-Bi to utilize visible light.

3. Simulating dye residues in wastewater by using Methylene Blue (MB) solution to co-dope and mono-dope g-C for bimetallic Sm and Bi₃N₄Prepared sample and pure g-C₃N₄And carrying out photocatalytic degradation activity test. g-C within 90min of illumination₃N₄The degradation rate of-Sm (4%) -Bi (4%) to MB is up to 90.34%, and the degradation rate is pure g-C₃N₄1.5 times of the total weight of the powder.

4. g-C is prepared from 10g of urea, melamine and urea mixed in proportion₃N₄By induction of the corresponding preparation of g-C₃N₄The results show that when the ratio of urea to melamine is 6:4, g-C is prepared₃N₄The effect of (A) is most ideal.

Drawings

FIG. 1a samples g-C₃N₄、g-C₃N₄-Sm、g-C₃N₄-Bi、g-C₃N₄-XRD pattern of Sm — Bi;

FIG. 1b XRD pattern enlarged to 20-35 in FIG. 1 a;

FIG. 2 samples g-C₃N₄、g-C₃N₄-Bi、g-C₃N₄-Sm、g-C₃N₄FTIR chart of Sm-Bi;

FIG. 3 self-made photodegradation simulation test equipment

FIG. 4 g-C of several starting materials₃N₄Photocatalytic activity comparison graph;

FIG. 5 shows that different doping amounts Sm are doped with g-C₃N₄Comparative photo-degradation activity of (a);

FIG. 6 preparation of g-C by co-doping Bi of different masses with 4% Sm₃N₄Comparing the catalytic activity of (1);

FIG. 7a is a graph comparing the photocatalytic activity effect of catalysts prepared by doping carbon nitride with different components;

FIG. 7b is a first order kinetic fit of the chemical kinetics of the four sets of samples of FIG. 7a to the photodegradation history of the MB solution;

FIG. 8a variation of MB degradation rate for catalysts prepared at different calcination temperatures;

FIG. 8b is an enlarged view of the box in FIG. 8 a;

FIG. 9a variation of MB degradation rate for catalysts prepared at different calcination time periods;

figure 9b is an enlarged view of the box in figure 9 a.

Reference numerals in fig. 3 denote: 1-xenon lamp; 2-a magnetic stirrer; 3-a water inlet; 4-water outlet.

Detailed Description

First part, monomers g-C₃N₄Samarium doped g-C₃N₄Bismuth doped g-C₃N₄Bimetallic element co-doped g-C₃N₄Preparation of the Material

1. Instruments and reagents

1.1, experimental apparatus: the main experimental apparatus is shown in table 1.

TABLE 1

Device name	Model number	Manufacturer of the product
			Electronic analytical balance	PL303	Mettler-Tollido instruments plant
Constant temperature heating magnetic stirrer	DF-101S	Medical instrument factory of gold jar city
			Baking oven	GZX-9140MBE	Shanghai Bocheng industries Ltd
Tubular vacuum furnace	BTF-1200C	ANHUI BEQ EQUIPMENT TECHNOLOGY Co.,Ltd.
			Xenon lamp	GXZ500W	Shanghai season light special lighting electrical equipment factory
Low-rotation-speed table type centrifuge	XL5A	HUNAN CENLEE SCIENTIFIC INSTRUMENTS Co.,Ltd.
			Ultraviolet-visible spectrophotometer	TU-1901	General instruments of Beijing Primel Ltd
X-ray diffractometer	D8Advance	Bruker, Germany
			Fourier infrared spectrometer	IRTACER-100	Shimadzu Japan Ltd

1.2, experimental materials, as shown in Table 2.

TABLE 2

Name of raw materials	Chemical formula (II)	Grade	Manufacturer of the product
				Urea	H₂NCONH₂	AR,90％	TIANJIN ZHIYUAN CHEMICAL REAGENT Co.,Ltd.
Melamine	C₃N₆H₆	AR,99％	Shanghai Aladdin Biotechnology Ltd
				Samarium (III) nitrate hexahydrate	SmN₃O₉·6H₂O	AR,99.99％	Shanghai Aladdin Biotechnology Ltd
Bismuth (III) nitrate pentahydrate	BiN₃O₉·5H₂O	AR,99.99％	Shanghai Aladdin Biotechnology Ltd
				Methylene blue	C₁₆H₁₈CIN₃S	AR,99.99％	Tianjin Haixin chemical industry Co., Ltd

2. Preparation of photocatalytic Material

2.1, monomersg-C₃N₄Preparation of the photocatalyst

An electronic analytical balance is operated to respectively weigh 10g of melamine, 10g of urea and 10g of a mixture of urea and melamine, wherein the proportions of the five groups of melamine are respectively 20%, 40%, 50%, 60% and 80%. And then, dividing each group of weighed raw materials into four equal parts, putting the four equal parts into four clean anhydrous magnetic boats, and symmetrically placing the four magnetic boats on two sides of the axis of the tube furnace. Setting the temperature rise rate of a tubular furnace to be 5 ℃/min, and carrying out constant-temperature calcination reaction at the high temperature of 550 ℃ for 4h to prepare pure monomer g-C₃N₄And then, grinding the calcined finished product into fine powder by using an agate mortar, and bagging for later use.

As shown in Table 3, g-C of melamine and urea in different ratios₃N₄The photocatalyst of (1).

TABLE 3

Melamine and urea ratios in 10g of calcined raw material	Melamine (g)	Urea (g)
			0% melamine 100% urea	0	10
20% melamine 80% urea	2	8
			40% melamine 60% urea	4	6
50% melamine 50% urea	5	5
			60% melamine 40% urea	6	4
80% melamine 20% urea	8	2
			100% melamine 0% urea	10	0

2.2 samarium doping g-C₃N₄And bismuth-doped g-C₃N₄Preparation of the photocatalyst

When samarium nitrate is used as a single component to dope g-C₃N₄When the composite photocatalyst material is synthesized, firstly, weighing ten groups of 6g of urea and 4g of melamine, then sequentially weighing ten groups of samarium nitrate with the mass of 0.1-1.0g, finally, respectively adding a mixture of the ten groups of urea and melamine weighed in advance into the ten groups of samarium nitrate with different masses, dissolving the samarium nitrate in a beaker filled with 60mL of deionized distilled water, then placing the samarium nitrate on a constant-temperature magnetic electric stirrer to stir at room temperature for 30min, fully and uniformly mixing the components, adjusting the temperature of the constant-temperature heating magnetic stirrer to 80 ℃, stirring and heating at constant temperature until all water is evaporated to dryness, and integrally presenting a solidified state. Then placing the beaker in a GZX-9140MBE type oven adjusted to 100 ℃ for drying again, taking out a sample dried into blocks after 4 hours (when taking out the sample, a scraper is used for lightly touching the wall of the beaker), grinding the sample into powder by using an agate mortar, and dividing the powder into equal parts to be placedPlacing the magnetic boat on two sides of the central axis of a BTF-1200C type tubular vacuum furnace (preventing the sample from being burnt in the calcining process to cause the failure of the experiment) for high-temperature calcining, and setting relevant parameters of the tubular furnace as follows: the calcining temperature is 550 ℃, the heating rate is 5 ℃/min, and the constant-temperature calcining time is 4 h. And after the vacuum tube furnace is calcined, cooling to below 100 ℃, taking out the sample, grinding the sample into powder, and filling the powder into a small-size sealed bag for storage for later use.

For single-component bismuth nitrate doping synthesis Bi-g-C₃N₄The preparation process of the composite photocatalytic degradation material is repeated.

2.3 preparation of bimetallic element codoped g-C3N4 photocatalyst

When the bimetallic element samarium and bismuth are jointly doped with g-C₃N₄When the composite photocatalyst material is synthesized, firstly, ten groups of 6g of urea and 4g of melamine are weighed, and then according to the m [ Sm (NO)₃)₃]:m[Bi(NO₃)₃]The mass ratios of (0.4:0.1, 0.4:0.2, 0.4:0.3, 0.4:0.4, 0.4:0.5, 0.4:0.6, 0.4:0.7, 0.4:0.8, 0.4:0.9 and 0.4:1.0) are sequentially weighed, finally, the weighed mixtures of the ten groups of urea and melamine are respectively mixed into the mixtures of the ten groups of samarium and bismuth, and the other experimental operation steps are the same as 2.2.

Second, structural characterization of composite photocatalyst

The method comprises the following steps of (1) characterizing the crystal phase structure of a sample by XRD (X-ray diffraction) under the conditions that the scanning speed is 0.1sec/step and the scanning range is 10-80 degrees by taking Cu Kalpha as a radiation source; and FT-IR is adopted to scan 500cm at the scanning range of 4000-^-1The precision is 0.0001cm^-1And the mass structure and intermolecular interaction of the catalyst were analyzed at a rate of 32 times/min.

1. X-ray diffraction (XRD) analysis

In order to further research the introduction of the bimetallic elements of samarium and bismuth to the g-C₃N₄Effect of basic Crystal Structure on photocatalyst g-C₃N₄、g-C₃N₄-Sm、g-C₃N₄-Bi、g-C₃N₄XRD spectrogram analysis of-Sm-Bi and other samplesAs shown in fig. 1a and 1 b.

As can be seen from FIG. 1a, the pure groups g-C₃N₄The crystal structure of (a) shows characteristic peaks at 13.1 ° and 27.5 °. The relatively weak peak is at 13.1 deg., which is attributed to the (100) plane peak, which is g-C₃N₄In-layer hole spacing diffraction peaks formed by carbon and nitrogen six-membered ring 3-s triazine structural units in a planar two-dimensional framework, and strong peaks belong to g-C₃N₄The peak of (002) face of (g) is g-C₃N₄An interslice signature diffraction peak. And the photocatalyst sample g-C doped with a metal element₃N₄-Sm、g-C₃N₄-Bi and g-C₃N₄The Sm-Bi also shows the two typical diffraction peaks, and each group of catalyst samples form a stronger diffraction peak near the 27.5 DEG position, and a weak peak appears or almost disappears at the position of about 13.1 deg. With pure g-C₃N₄A careful comparison of the samples shows that the metal-doped photocatalysts all change the peak intensity of the characteristic diffraction peak to some extent (see FIG. 1b), wherein the catalyst samples g-C₃N₄-Sm-Bi having the weakest intensity of characteristic diffraction peak at 27.5 DEG, g-C₃N₄-Sm times, g-C₃N₄-Bi of another, pure g-C₃N₄The peak intensity of (a) is highest.

g-C prepared by co-doping bimetallic element₃N₄The peak intensity of Sm-Bi at 27.5 ℃ is reduced and the peak at 13.1 ℃ is disappeared, indicating that samarium and bismuth atoms are uniformly embedded in the polymer skeleton, i.e. Sm/Bi/g-C is successfully prepared₃N₄A composite photocatalyst material. g-C₃N₄The strength of the characteristic peak of-Sm-Bi near 13.1 ℃ and 27.5 ℃ is weakened, which is caused by the influence of the co-doping of bimetallic element samarium and bismuth on g-C₃N₄Complete polymerization under high temperature conditions. Even though the characteristic peak intensity is reduced, the general peak shape and peak position of the pure component graphite phase carbon nitride are contrasted, and the bimetallic co-doped synthesized photocatalytic material g-C is not observed₃N₄The diffraction peak orientation of Sm-Bi is significantly changed, indicating that doped g-C can also be formed in the presence of metal ions₃N₄The basic structure does not need to change the original graphite-like basic skeleton of the carbonitride, so that the g-C is not changed by doping the metal elements₃N₄The arrangement structure of the basic crystal form can only change a few structural segments in a small range, and the weak structural change does not influence the number of the photocatalytic reaction active sites of the carbon nitride and simultaneously does not weaken the photocatalytic degradation capability of the carbon nitride. Namely the introduction of Sm and Bi to g-C on a two-dimensional plane₃N₄The crystal structure and photocatalytic activity of the ligand have no negative effect.

2. Fourier Infrared Spectroscopy (FT-IR) analysis

As can be seen in FIG. 2, at 820cm^-1And 1250-^-1The areas of (A) and (B) show vibration peaks which are respectively compared with vibration peak ranges caused by respiratory vibration and stretching vibration of a carbon-nitrogen six-membered ring, which shows that the four groups of catalyst samples all show the vibration peaks of the carbon-nitrogen triazine heterocyclic ring skeleton unique to graphite-phase carbon nitride. And is at 3150 and 3350cm^-1The left and right vibrational peaks are due to-OH and-NH stretching vibrations, which are respectively derived from water molecules adsorbed by the sample and unpolymerized amine groups on the surface of the catalyst sample. Samples g-C₃N₄-Sm、g-C₃N₄-Sm-Bi in 2200cm^-1The vibration peak appeared nearby is attributed to the stretching vibration of the azide, and the vibration peak is gradually increased along with the co-doping of Sm and Bi, so that Sm and Bi are co-doped to possibly form an Sm-Bi chemical bond. In addition, comparison of the FT-IR spectra of four catalyst samples, except at 2200cm^-1Except for the difference of nearby vibration peaks, single metal doping or double metal co-doping g-C₃N₄The catalyst prepared is mixed with the pure components g-C₃N₄The FT-IR spectrum of the catalyst was almost the same as that of the catalyst at 1900cm^-1The intensity of the absorption peak at a location varies only by a small amount. This shows that the co-doping of the bimetal Sm and Bi does not obviously change g-C₃N₄The Sm and Bi codoping effectively strengthens the photodegradation performance of the catalyst to dye pollutants, and simultaneously still maintains the g-C₃N₄Chemical junction ofHas the advantages.

Third fraction, monomers g-C₃N₄Samarium doped g-C₃N₄Bismuth doped g-C₃N₄Bimetallic element co-doped g-C₃N₄Photocatalytic performance study of materials

The degradation performance of the catalyst sample on the dye pollutants was determined by using a home-made photocatalytic degradation simulation test device as shown in fig. 3, and the detailed test procedure was to weigh 10mg of the photocatalyst sample into a (50mL, 0.02g/L) Methylene Blue (MB) aqueous solution using an analytical balance, and place the mixture suspension in a dark environment and magnetically stir for 30min before turning on the xenon lamp 1 to saturate the adsorption-desorption state between the photocatalyst sample and the MB aqueous solution. And then continuing to stir the reaction solution 2 by using the magnetic force, simultaneously turning on the xenon lamp 1 to continuously illuminate for 90min, using a liquid transfer gun to transfer 4mL of the reaction solution every 15min, and placing the reaction solution into a centrifuge tube and numbering the reaction solution for later use. After the photocatalytic degradation experiment is completed, in order to further evaluate the photocatalytic performance, a low-rotation-speed desktop centrifuge is used at a rotation speed of 3000 r-min-¹The sampled solution was centrifuged for 1min under the conditions described above to precipitate photocatalyst particles suspended in the MB solution, and after the upper layer impurity-free solution was absorbed by a rubber-tipped dropper, the absorbance of the remaining MB solution after photodegradation was measured at 664nm using a single-beam visible spectrophotometer model TU-1901.

1. Statistical method

The initial concentration of MB is recorded as Co, the concentration of MB sampled at the time t is recorded as C, the photocatalytic degradation rate C/Co is taken as a y coordinate axis to make a line graph of the reaction time t, and the line graph can effectively and visually reflect the metal modified and doped g-C in the system₃N₄The prepared composite photocatalyst is used for simulating the degradation condition of dye pollutant MB. Wherein the percent degradation of the simulated pollutant MB solution can be calculated by the following mathematical formula:

2. g-C prepared from different starting materials₃N₄Photocatalytic activity

As shown in Table 3, the preparation of g-C from melamine and urea as base stocks₃N₄. The preparation method comprises the steps of respectively selecting 10g of 100% melamine, 10g of 100% urea and 20%, 40%, 50%, 60% and 80% of basic raw materials of melamine when the mass sum of the urea and the melamine is 10g, preparing the pure-component graphite-phase carbon nitride photocatalyst, and calcining at 550 ℃ in a vacuum tube furnace. As shown in table 4:

TABLE 4

After repeated experimental determination of photocatalytic degradation of MB solution, the degradation rate of the photocatalyst material prepared from the raw materials is respectively obtained: 38.41%, 52.11%, 54.61%, 61.43%, 46.79%, 42.07%, 42.64%. And the line graph of the degradation rate of the specific catalyst to the simulated pollutant MB solution changing with time in the photocatalytic degradation process is shown in figure 4.

The above experimental data show that:

preparation of g-C from pure melamine₃N₄The highest yield but the lowest photocatalytic degradation rate, which is only 38.41%.

② preparation of g-C by pure urea₃N₄The photocatalytic degradation rate of (A) was 52.11% second only to the yield of 40% of the highest melamine component, 61.43%, however, g-C was prepared from pure urea₃N₄The yield of the raw material for preparing the carbon nitride is only 5.83 percent at the lowest, which is caused by that the urea is carbonized in the high-temperature calcination process and releases a large amount of ammonia gas and carbon dioxide which are easy to volatilize, but when the melamine and the urea are mixed according to the proportion to prepare the g-C₃N₄On the one hand, the addition of urea increases the g-C produced₃N₄Specific surface area, preparation of g-C by modifying pure melamine₃N₄Undesirable photocatalytic effect, and on the other hand, the preparation of g-C by pure urea modified by melamine₃N₄The yield is extremely low, and the best effect is achieved after the two basic raw materials are mixed in proportion.

③ the addition of urea increases the degradation rate of the photocatalyst and reduces the yield because of the calcination of g-C at high temperature₃N₄When urea is decomposed by heating at high temperature, a large amount of carbonic anhydride and ammonia are formed because these gases are in g-C₃N₄The thermal polymerization proceeds by overflowing in the form of small bubbles, so that the carbon nitride forms a loose porous structure and the g-C increases with the urea doping content₃N₄The loose lamellar structure of the sample is more fluffy, the cavity of the sample is increased, namely the specific surface area is increased, and the g-C is widened₃N₄Receiving area of visible light, thereby improving g-C₃N₄Photocatalytic degradation activity of (1).

g-C prepared from components with melamine accounting for 20%, 50%, 80% and 60%₃N₄With the gradual addition of urea, the degradation rate of the catalyst slowly increases, but at the same time g-C₃N₄The yield of (a) decreases with a gradual decrease in the melamine ratio.

Fifthly, preparing g-C by using components with melamine accounting for 40 percent (namely m urea: m melamine is 6:4)₃N₄The photocatalytic degradation rate of the urea is 61.43 percent, and the yield of the catalyst reaches 31.02 percent, namely the best proportioning state after the melamine and the urea are mixed is achieved. Finally, the preparation g-C is finally determined after mixing urea melamine according to the mass ratio of 6:4₃N₄The basic raw material of (1).

3. Photocatalytic activity of Sm-doped g-C3N4 with different doping amounts

On one hand, the method explores the effective modification g-C of rare earth metal element samarium₃N₄The mechanism of photocatalytic performance; on the other hand, the method deeply researches the introduction of metal element samarium to synthesize the photocatalyst g-C₃N₄Optimum impurity doping amount ratio of Sm (X), where X is 1% -10%, by the experimental operation procedure of synthesizing photocatalytic material described above, a total of ten groups g-C are obtained₃N₄-Sm (X) material, as shown in FIG. 5, part of which is soluble in simulated pollutant methylene blueLine graph of degradation rate of liquid (MB) over time.

According to the photocatalytic degradation result shown in FIG. 5, when the value of X (X is the mass content of samarium) is less than 4%, g-C₃N₄The photocatalytic degradation effect of the Sm (X) sample on MB is increased in a gradient manner along with the further increase of the doping amount X of the metal Sm, and when the doping amount X is 4 percent, g-C₃N₄Sm (4%) had the best degradation effect on methylene blue MB solution, and the removal efficiency on MB solution was raised to 81.96% of the peak value of the line graph. However, when X is higher than 4%, g-C₃N₄The photocatalytic function of the Sm (X) sample on MB is gradually reduced along with the further increase of the doping amount X of the metal Sm. I.e. excess Sm doped g-C₃N₄The degradation of MB by the photocatalyst is not facilitated, because the excessive rare earth element Sm is recombined with the centers of electrons and holes to promote the recombination of photogenerated carriers, so that the photocatalyst g-C₃N₄The photocatalytic degradation rate of-Sm (5% -10%) on the MB solution is reduced.

Furthermore, as can be seen from FIG. 5, pure g-C₃N₄The photocatalytic degradation of MB is the worst, and g-C₃N₄The photocatalytic degradation rate of-Sm (4%) was 1.3 times that of-Sm. Therefore, the results of this part of the photocatalytic experiment show that: doping rare earth metal element samarium with g-C₃N₄Synthetic g-C₃N₄the-Sm photocatalyst can effectively modify g-C₃N₄The photocatalytic degradation activity of the catalyst is greatly improved; doping rare earth element samarium with g-C₃N₄Synthesis of photocatalytic sample g-C₃N₄The optimum amount of-Sm incorporated is 4%, i.e. g-C₃N₄the-Sm (4%) has the best photocatalytic effect, and has better photocatalytic degradation effect relative to pure g-C3N 4.

According to the photocatalysis result reflected by the figure 5 and the analysis by combining the XRD spectrogram, the g-C₃N₄-Sm has a mesoporous structure inside, which is comparable to the massive g-C₃N₄With a large variance. When visible light is irradiated to the catalyst surface, multiple refraction and scattering are caused. Such a porous structureThe adsorption and the profiling process of the residual small dye particles are more effective, and the photocatalytic degradation process is facilitated. And the mesoporous structure and the original monomer g-C with a smooth two-dimensional layered structure₃N₄In contrast, a structurally porous arrangement has more exposed geometric surfaces. Prompt g-C₃N₄Sm oxidant ratio g-C₃N₄Has more active sites, and can effectively improve the photocatalytic reaction speed of the material.

4. Preparation of g-C by co-doping Bi with different doping amounts and 4% of Sm₃N₄Photocatalytic activity

The part prepares ten groups of samarium-bismuth double-metal co-doped g-C₃N₄Preparation of g-C₃N₄-Sm (4%) -Bi (Y) (Y takes a value of 1% -10%) composite photocatalyst samples, and the degradation activity of ten groups of photocatalyst samples on the MB solution is measured, and the specific photocatalysis result is shown in figures 3-5. Doping g-C in single component of samarium metal₃N₄On the basis of preparing the photocatalyst, the addition of the metal element bismuth strengthens g-C₃N₄Degradation effect of the material on MB. When catalyst samples g-C₃N₄When the value of Y (Y is the mass content of Bi) in the-Sm (4%) -Bi (Y) is 1% -4%, the degradation rate of the sample catalyst to the simulated dye waste MB is gradually increased along with the increase of the doping amount of the metal bismuth (the photocatalytic degradation rate is 81.95%, 65.38%, 78.39%, 82.66% and 87.39% in sequence). And when the doping amount of the metal element bismuth is 4%, the removal rate of the photocatalyst sample to MB reaches a peak value of 87.39%, which is higher than that of the photocatalyst g-C₃N₄The degradation rate of-Sm (4%) was about 5.43% higher than 81.96%, but when the photocatalyst sample g-C₃N₄When the value of Y in-Sm (4%) -Bi (Y) is 5% -10%, the degradation rate of the catalyst to MB is gradually reduced along with the increase of the doping amount of the metal element bismuth (the photocatalytic degradation rate is 81.71%, 71.98%, 70.03%, 69.43%, 63.15% and 46.61% in sequence).

Therefore, the doping amount of the metal bismuth can change the degradation effect of the photocatalyst, and the moderate doping of the metal bismuth can obviously enhance the g-C₃N₄Photodegradation of MBProperties of the solution. However, excessive doping with bismuth metal can run counter to the desired effect. This may be excessive doping of the metal bismuth to block the g-C₃N₄The mesoporous structure of Sm results in the decrease of the absorption efficiency of the prepared photocatalyst on visible light, so that the degradation activity of the photocatalyst on MB solution is obviously weakened. Therefore, the experimental results show that g-C is doped in the single component of the rare earth metal element samarium₃N₄On the basis, the addition of the metal bismuth obviously improves the light removal rate of the material to the simulated organic pollutant MB. And, bimetallic co-doping of g-C₃N₄Preparation of composite photocatalyst g-C₃N₄The optimum doping amount of the metal bismuth is 4% for Sm-Bi, and samples g-C₃N₄The photocatalytic degradation rate of-Sm (4%) -Bi (4%) is up to 87.39% and is pure g-C₃N₄1.5 times of the photocatalyst.

5. First order kinetic fitting of chemical reactions

As shown in FIG. 7a, four groups of photocatalysts g-C were compared₃N₄、g-C₃N₄-Bi(4％)、g-C₃N₄-Sm(4％)、g-C₃N₄The photocatalytic degradation performance of-Sm (4%) -Bi (4%) on the MB solution within 2h, and the bimetallic codoping g-C can be seen from the graph₃N₄Preparation of g-C₃N₄the-Sm (4%) -Bi (4%) catalyst has optimal photocatalytic degradation effect, and the photocatalytic degradation rate is pure g-C respectively₃N₄、g-C₃N₄-Bi(4％)、g-C₃N₄1.42 times, 1.37 times and 1.1 times of-Sm (4%), etc. Meanwhile, in order to more intuitively reflect the photocatalytic degradation activity of the four groups of samples on the MB, a first-order chemical dynamics fitting curve of the four groups of samples on the photodegradation process of the MB solution is further drawn.

When the concentration of MB is low, its function of concentration change with time in the course of being decomposed coincides with the rule of the quasi-first order reaction kinetics simulation curve, and thus it is fitted using the chemical first order reaction kinetics equation, as shown in FIG. 7 b. As can be seen from the figure, on the one hand, pure g-C synthesized without doping with metal elements₃N₄The rate constant of the photocatalytic degradation reaction is lowest, and samarium and bismuth are doped with g-C₃N₄Preparation of g-C₃N₄-Sm(4％)、g-C₃N₄The reaction rate constant of-Bi (4%) is significantly higher than that of pure g-C₃N₄This shows that single metal elements of samarium and bismuth are successfully doped in g-C₃N₄In addition, g-C is effectively strengthened₃N₄The photocatalytic degradation effect of the metal is that on the other hand, the bimetal samarium bismuth is codoped with g-C₃N₄Prepared composite photocatalytic material g-C₃N₄The photocatalytic reaction rate constant of-Sm (4%) -Bi (4%) is up to 0.02362h^-1Purer g-C₃N₄Is higher than 0.01311h^-1g-C doped with a single component metal₃N₄Synthetic materials g-C₃N₄Bi (4%) is higher than 0.01300h^-1Ratio g-C₃N₄-Sm (4%) is higher than 0.00483h^-1Left and right. Thus, the above experimental data fully demonstrate g-C₃N₄The (4%) of-Sm and (4%) of-Bi greatly improve the g-C₃N₄The photocatalytic degradation efficiency of (a).

6. Calcination temperature vs. catalyst g-C₃N₄Effect of the photocatalytic Activity of-Sm-Bi

FIGS. 8a and 8b show the calcination temperatures for 4h for catalyst samples g-C₃N₄-Sm

(4%) -Bi (4%) degraded the line graph of the MB solution. As is clear from the graph, the effect of photocatalytic degradation of MB was relatively excellent when the calcination temperature was controlled to 550 ℃ with the calcination time being controlled to 4 hours, and the photocatalytic degradation rate of the catalyst was increased in a gradient manner as the calcination temperature was increased from 530 ℃ to 550 ℃, but was gradually decreased in a gradient manner as the calcination temperature was increased from 550 ℃ to 580 ℃. This shows that 550 ℃ is both a peak value and a defined value, i.e. less than 550 ℃, the stronger the photocatalytic performance of the prepared catalyst is with the increase of temperature, and vice versa when the temperature is more than 550 ℃. Therefore, when the calcination time is fixed and the calcination temperature is 550 ℃, the calcination effect of the photocatalyst is optimal.

7. Calcination time vs. g-C₃N₄Effect of the photocatalytic Activity of-Sm-Bi

FIGS. 9a and 9b show different calcination times at 550 ℃ for catalyst samples g-C₃N₄-Sm (4%) -Bi (4%) degraded the line graph of MB solution. As can be seen from the figure, the calcination temperature is kept consistent, the catalyst has the best effect on the degradation of MB when the calcination time is 3h, and the photocatalytic degradation rate of the catalyst increases in a gradient manner when the calcination time is prolonged from 1h to 3h, but the photocatalytic degradation rate of the catalyst decreases in a gradient manner when the calcination temperature is prolonged from 3h to 6 h. When the calcination temperature is relatively lower or the calcination time is relatively shorter, the crystallinity of the photocatalyst is relatively lower, and the photoproduction electrons and the holes are easy to recombine, namely the photocatalytic activity is deviated; when the calcination temperature is high or the calcination time is long, the particle diameter of the photocatalytic material is increased, and the active sites of the catalyst are reduced, so that the photocatalytic effect is reduced. Thus, the above experimental data show that when the calcination temperature of the tube furnace is set to 550 ℃ and the calcination time is set to 3 hours, the bimetal co-dopes g-C₃N₄Preparation of g-C₃N₄The degradation rate of the-Sm-Bi composite photocatalyst is the most ideal and reaches 90.34%.

Third part, conclusion

Pure g-C₃N₄Based on the structural characteristics of the naked carbon nitride, the specific surface area is low, the photogeneration-electron recombination rate is high, the utilization rate of visible light is low, and the photocatalytic degradation activity of the material is limited^[33]. Under the condition, the g-C can be effectively overcome by co-doping the bimetallic elements Sm and Bi₃N₄Of (2) to (2). The bimetal Sm and Bi codoped g-C is prepared by high-temperature calcination thermal condensation of melamine and urea in the presence of metal salt by adopting a high-temperature one-step calcination method₃N₄g-C3N 4-Sm-Bi.

(1) The optimal mixture ratio of mixed melamine and urea, Sm and Bi single component metal doped g-C is explored₃N₄BimetalCodoping of g-C₃N₄The optimum doping quality, and the influence of the calcination temperature and the calcination time on the activity of the photodegradation simulation pollutant of the catalyst. Experimental results show that when the calcining temperature is 550 ℃, the calcining time is 3 hours, the mass ratio of urea to melamine is 6:4, and the mass ratio of Sm to Bi codoped is 4% to 4%, the photocatalysis effect is optimal, and the prepared photocatalyst g-C₃N₄-Sm (4%) -Bi (4%) for MB (10 mg/L) after 90min of continuous irradiation^-1) The degradation rate of the product reaches 90.34 percent, and the product is pure g-C₃N₄1.5 times of the total weight of the powder.

(2) The results of spectral characterization such as XRD and FT-IR are combined, and the co-doping of the bimetallic Sm and the bimetallic Bi does not change g-C₃N₄The graphite phase structure of (2), but does reduce the g-C₃N₄The specific surface area of the photocatalyst is increased, the recombination of photo-generated charge carriers is inhibited, and the degradation performance of the photocatalyst on a simulated organic pollutant MB solution is further enhanced.

In conclusion, the combination of the structural characterization and photocatalytic performance evaluation of the catalyst proves that the g-C with good stability and excellent photocatalytic degradation activity is synthesized by a simple calcination method₃N₄-Sm (4%) -Bi (4%) photocatalyst.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications are possible which remain within the scope of the appended claims.

Claims

1. The preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material is characterized by comprising the following steps of:

(3) then drying in an oven, cooling and grinding into powder;

2. The preparation method of the bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material of claim 1, wherein in step (1): the mass sum of melamine and/or urea is 10g, and the mass ratio of melamine to urea is 10:0, 8:2, 6:4, 5:5, 4:6, 2:8 and 0: 10.

3. The method for preparing the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material of claim 1, wherein the soluble samarium salt is samarium nitrate and the soluble bismuth salt is bismuth nitrate.

4. The method for preparing the bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material as claimed in claim 3, wherein the mass ratio of samarium nitrate to bismuth nitrate is 0.4: (0.1-1.0).

5. The preparation method of the bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material of claim 1, wherein in step (1): the mixture of melamine and/or urea and the mixture of soluble samarium salt and soluble bismuth salt are dissolved in a beaker filled with 60mL of deionized distilled water, and then the beaker is placed on a constant-temperature magnetic electric stirrer to stir at room temperature for 30min, and all the components are fully and uniformly mixed.

6. The method for preparing the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material as claimed in claim 1, wherein in step (2), the temperature of the constant temperature heating magnetic stirrer is adjusted to 80 ℃, the constant temperature stirring and heating are carried out until all water is evaporated to dryness, and the whole material is in a solidified state.

7. The method for preparing the bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material of claim 1, wherein in step (3), the beaker in step (2) is placed in an oven adjusted to a temperature of 100 ℃ for drying, and after 4 hours, the dried sample is taken out and ground into powder by using an agate mortar.

8. The preparation method of the bimetal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material of claim 1, wherein in step (4), the calcination parameters of the tubular vacuum furnace are as follows: the calcining temperature is 550 ℃, the heating rate is 5 ℃/min, and the constant-temperature calcining time is 4 h; cooling to below 100 ℃ after the vacuum tube furnace is calcined, taking out the sample and grinding the sample into powder to obtain g-C co-doped with the bimetallic elements of samarium and bismuth₃N₄Synthesizing the composite photocatalyst material.

9. The application of the bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material prepared according to any one of claims 1 to 8 in photocatalytic degradation, wherein the bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material can be used for photocatalytic degradation of methylene blue under a photocatalytic condition.