CN111939963B - Preparation method of Bi-metal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of Bi-metal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material in photocatalytic degradation - Google Patents
Preparation method of Bi-metal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of Bi-metal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material in photocatalytic degradation Download PDFInfo
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Images
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
-
- B01J35/39—
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/30—Treatment of water, waste water, or sewage by irradiation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/30—Organic compounds
- C02F2101/308—Dyes; Colorants; Fluorescent agents
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/30—Organic compounds
- C02F2101/40—Organic compounds containing sulfur
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2305/00—Use of specific compounds during water treatment
- C02F2305/10—Photocatalysts
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/30—Wastewater or sewage treatment systems using renewable energies
- Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy
Abstract
The invention discloses a preparation method of a Bi-metal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of photocatalytic degradation, which comprises the steps of mixing a mixture of melamine and/or urea with a mixture of samarium salt and bismuth salt, and dissolving the mixture in deionized water under magnetic stirring at room temperature; heating to dry the water under stirring; drying in an oven, cooling, and grinding into powder; placing the powder sample in a tubular vacuum furnace, calcining at high temperature, cooling, and grinding into powder to obtain the bimetal element samarium and bismuth co-doped g-C 3 N 4 Synthesizing the composite photocatalyst material. Co-doping of the bimetal in unchanged g-C 3 N 4 The structure increases the specific surface area of the catalyst, inhibits the recombination of photo-generated charge carriers and improves the catalyst g-C 3 N 4 -Sm-Bi availability to visible light; g-C 3 N 4 The degradation rate of Sm-Bi to MB is up to 90.34 percent, and the Sm-Bi is pure g-C 3 N 4 1.5 times of (2).
Description
Technical Field
The invention relates to the technical field of preparation of photocatalytic materials. In particular to a preparation method of a Bi-metal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material and application of photocatalytic degradation.
Background
Since the innovation was opened, industrial science and technology have been improved dramatically in the age background of the development of socioeconomic performance, but at the same time, the double-edged sword has also posed a series of ecological environmental threats including serious challenges of energy failure, dye wastewater pollution, atmospheric ozone layer cavity and the like. The Chinese is a country with strong dye manufacture and consumption, and a large amount of waste dye residues in the printing and dyeing industry cause the water body to be widely polluted, thus causing serious threat to human health. Therefore, how to solve the problem of dye pollution efficiently and without public hazard has been gradually developed as an important research content in the current environmental protection category.
In various dye degradation technologies, the photocatalytic technology has strong capability of catalyzing and degrading pollutants, few side effects on the environment and other bright spots, and in recent years, an emerging organic polymer semiconductor, namely graphite-like carbon nitride (g-C) 3 N 4 ) Is considered as a novel visible light catalyst. Due to the outstanding advantages of graphite-phase carbon nitride such as simple preparation process, the graphite-phase carbon nitride has a lamellar structure similar to graphite and a matched conduction band valence band position (g-C 3 N 4 The band gap width of 2.7 eV) and stable chemical and physical properties, the catalyst has been rapidly developed as a focus of research field of degrading organic pollutants by nonmetallic photocatalysts.
But original g-C 3 N 4 There are bottlenecks such as too low specific surface area, wide energy band gap, ultraviolet and visible light absorption, rapid recombination of photo-generated electron-hole pairs, unsatisfactory photocatalytic degradation effect, too low recycling rate and the like. Based on this, experts have explored various methods to improve g-C 3 N 4 The photocatalytic degradation effect is summarized in three aspects: (1) broadening g-C 3 N 4 The exposed specific surface area between the sheets; (2) reducing g-C by adopting a doping modification mode 3 N 4 Is extended by g-C 3 N 4 A response range to visible light; (3) construction of various semiconductors and g-C 3 N 4 Heterojunction composite photocatalyst. Specific to g-C 3 N 4 The modification measures of the method comprise five modes including non-metal element doping, noble metal element deposition or non-noble metal element doping, dye sensitization, stripping of single layers and compounding of semiconductor materials. Wherein the metal doping is the easiest and excellent one capable of improving g-C 3 N 4 Modification of photocatalytic ActivityMeans of the method. However, so far, the modification of carbon nitride has been mostly carried out by single noble metal, non-noble metal doping or noble metal doping, such as Li Peng, etc. to carry out metal doping of g-C 3 N 4 Is prepared by non-noble metal Ni doping g-C by theoretical research of Puhui Deng 3 N 4 Research on catalysts, zhouchen, et al performed Ag doping optimization of g-C 3 N 4 But there are still many works like bi-metal co-doping, rare earth metal and non-noble metal co-doping, etc. there has been no intensive study.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to provide the preparation and photocatalytic degradation application of the bimetallic Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material which can remarkably reduce the combination efficiency of photo-generated electron holes and widen the absorption range of the bimetallic Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material in a narrower visible light irradiation area, and the degradation performance of the bimetallic 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 Bi-metal Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material comprises the following steps:
(1) Mixing melamine and/or urea with a mixture of a soluble samarium salt and a soluble bismuth salt, and then dissolving in deionized water under magnetic stirring at room temperature;
(2) Heating to dry by stirring, and solidifying;
(3) Then placing the mixture in an oven for drying, cooling and grinding the mixture into powder;
(4) Placing the powder sample in a tubular vacuum furnace, calcining at high temperature, cooling, and grinding into powder to obtain the bimetal element samarium and bismuth co-doped g-C 3 N 4 Synthesizing the composite photocatalyst material.
The preparation method of the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material comprises the following steps of: the sum of the masses 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.
The preparation method of the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material comprises the steps that the soluble samarium salt is samarium nitrate, and the soluble bismuth salt is bismuth nitrate.
The preparation method of the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material comprises the following steps of: (0.1-1.0).
The preparation method of the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material comprises the following steps of: the mixture of melamine and/or urea and the mixture of soluble samarium salt and soluble bismuth salt were dissolved in a beaker containing 60mL of deionized distilled water, followed by placing on a constant temperature magnetomotive electric stirrer and stirring at room temperature for 30min, and the components were thoroughly and uniformly mixed.
In the step (2), the temperature of the constant-temperature heating magnetic stirrer is adjusted to 80 ℃, the mixture is stirred and heated at constant temperature until all water is evaporated to dryness, and the whole body 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, a sample dried into blocks is taken out after 4 hours, and the sample is ground into powder by using an agate mortar.
In the preparation method of the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material, in the step (4), the calcination parameters of a tubular vacuum furnace are as follows: calcining at 550 ℃ at a temperature rising speed of 5 ℃/min for 4 hours at constant temperature; cooling to below 100deg.C after calcining in vacuum tube furnace, taking out sample, grinding into powder to obtain bimetal element samarium and bismuth doped g-C 3 N 4 Synthesizing the composite photocatalyst material.
The prepared Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material can be used for carrying out photocatalytic degradation on methylene blue under the photocatalytic condition.
The technical scheme of the invention has the following beneficial technical effects:
1. adopts a one-step high-temperature calcination method to prepare the bimetal Sm-Bi co-doped g-C 3 N 4 The composite photocatalyst of the preparation method selects characterization means such as XRD, FT-IR and the like to analyze the structure and the morphology of the prepared sample.
2. Co-doping of the bimetal in unchanged g-C 3 N 4 The structure effectively reduces the forbidden bandwidth of the carbon nitride, increases the specific surface area of the catalyst by reducing the limitation of the catalyst on the visible light response, inhibits the recombination of photo-generated charge carriers and further improves the catalyst g-C 3 N 4 -Sm-Bi availability to visible light.
3. Dye residues in wastewater are simulated by Methylene Blue (MB) solution, and double metals Sm and Bi are co-doped and single doping g-C is performed 3 N 4 Prepared sample and pure g-C 3 N 4 Photocatalytic degradation activity was tested. Illumination for 90min, g-C 3 N 4 Sm (4%) -Bi (4%) has a degradation rate of up to 90.34% on MB, and is pure g-C 3 N 4 1.5 times of (2).
4. Preparation of g-C from 10g of urea, melamine and urea in a proportional mixing 3 N 4 In the way of (2) and summarize the corresponding production of g-C 3 N 4 The results show that g-C is prepared when the ratio of urea to melamine is 6:4 3 N 4 The effect of (2) is most ideal.
Drawings
FIG. 1a sample g-C 3 N 4 、g-C 3 N 4 -Sm、g-C 3 N 4 -Bi、g-C 3 N 4 -XRD pattern of Sm-Bi;
the XRD pattern of FIG. 1b, FIG. 1a, is enlarged to 20-35;
FIG. 2 sample g-C 3 N 4 、g-C 3 N 4 -Bi、g-C 3 N 4 -Sm、g-C 3 N 4 F of Sm-BiA TIR map;
FIG. 3 self-made photodegradation simulation test equipment
FIG. 4 g-C prepared from several starting materials 3 N 4 A comparative graph of photocatalytic activity;
FIG. 5 Sm g-C at different doping levels 3 N 4 Is a comparison of photodegradation activity of (2);
FIG. 6 Co-doping Bi of different masses with 4% Sm to prepare g-C 3 N 4 Is a comparison of the catalytic activity of (a);
FIG. 7a is a graph comparing the photocatalytic activity effects of catalysts prepared by doping carbon nitride with different components;
FIG. 7b is a plot of the chemical first order kinetics of the photodegradation of MB solution for the four sets of samples of FIG. 7 a;
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 with different calcination durations;
fig. 9b is an enlarged view of the block in fig. 9 a.
The reference numerals in fig. 3 are denoted as: 1-xenon lamp; 2-a magnetic stirrer; 3-a water inlet; 4-water outlet.
Detailed Description
First part, monomer g-C 3 N 4 Samarium doped g-C 3 N 4 Bismuth doped g-C 3 N 4 Co-doping of bimetal element g-C 3 N 4 Preparation of the Material
1. Instrument and reagent
1.1, experimental instrument: the main laboratory instruments are shown in table 1.
TABLE 1
| Device name | Model number | Manufacturing factories |
| Electronic analytical balance | PL303 | Metrele-Toli Multi Instrument works |
| Constant temperature heating magnetic stirrer | DF-101S | Medical instrument factory in gold altar market |
| Baking oven | GZX-9140MBE | Shanghai Bo Xingjingxiao Co., ltd |
| Tubular vacuum furnace | BTF-1200C | ANHUI BEQ EQUIPMENT TECHNOLOGY Co.,Ltd. |
| Xenon lamp | GXZ500W | Shanghai Ji Guang special lighting electric appliance factory |
| Low-rotation-speed desk type centrifugal machine | XL5A | HUNAN CENLEE SCIENTIFIC INSTRUMENTS Co.,Ltd. |
| Ultraviolet-visible spectrophotometer | TU-1901 | Beijing general analysis general instruments Co., ltd |
| X-ray diffractometer | D8Advance | Bruker Germany |
| Fourier infrared spectrometer | IRTACER-100 | Shimadzu corporation of Japan |
1.2, experimental materials, as shown in Table 2.
TABLE 2
| Raw material name | Chemical formula | Grade | Manufacturer(s) |
| Urea | H 2 NCONH 2 | AR,90％ | TIANJIN ZHIYUAN CHEMICAL REAGENT Co.,Ltd. |
| Melamine | C 3 N 6 H 6 | AR,99％ | Shanghai Aba Ding Shenghua technologies Co.Ltd |
| Samarium (III) nitrate hexahydrate | SmN 3 O 9 ·6H 2 O | AR,99.99％ | Shanghai Aba Ding Shenghua technologies Co.Ltd |
| Bismuth (III) nitrate pentahydrate | BiN 3 O 9 ·5H 2 O | AR,99.99％ | Shanghai Aba Ding Shenghua technologies Co.Ltd |
| Methylene blue | C 16 H 18 CIN 3 S | AR,99.99％ | Tianjin, sea letter chemical industry Co.Ltd |
2. Preparation of photocatalytic materials
2.1, monomer g-C 3 N 4 Photocatalyst preparation of (a)
10g of melamine, 10g of urea and 10g of a mixture of 10g of urea and melamine, which respectively account for 20%, 40%, 50%, 60% and 80% of five groups of melamine, are weighed equally in an operation electronic analysis day. 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 central axis of the tube furnace. Setting the heating rate of a tube furnace to be 5 ℃/min, and calcining at a constant temperature of 550 ℃ for 4 hours to prepare pure monomer g-C 3 N 4 And then grinding the calcined finished product into fine powder by using an agate mortar for later use.
As shown in Table 3, the g-C of melamine and urea with different proportions 3 N 4 Is a photocatalyst of (a).
TABLE 3 Table 3
| Melamine and urea ratio in 10g calcined raw material | Melamine (g) | Urea (g) |
| 0 |
0 | 10 |
| 20 |
2 | 8 |
| 40 |
4 | 6 |
| 50 |
5 | 5 |
| 60 |
6 | 4 |
| 80 |
8 | 2 |
| 100 |
10 | 0 |
2.2 samarium doped g-C 3 N 4 And bismuth doped g-C 3 N 4 Photocatalyst preparation of (a)
When samarium nitrate is used as a single component to dope g-C 3 N 4 When the composite photocatalyst material is synthesized, firstly weighing ten groups of 6g urea and 4g melamine, then sequentially weighing ten groups of samarium nitrate with the mass of 0.1-1.0g, finally adding the mixture of ten groups of urea and melamine which are weighed in advance into ten groups of samarium nitrate with different mass respectively, dissolving the mixture into a beaker filled with 60mL deionized distilled water, then placing the mixture on a constant-temperature magnetic electric stirrer, stirring the mixture for 30min at room temperature, and after the components are fully and uniformly mixed, regulating the temperature of the constant-temperature heating magnetic stirrer to 80 ℃, stirring the mixture at constant temperature, heating the mixture to all moisture, and evaporating the mixture to dryness, thereby obtaining the whole solidified state. Then placing the beaker in a GZX-9140MBE type oven with the temperature being adjusted to be 100 ℃ for drying again, taking out a sample dried into blocks after 4 hours (a scraper is used for lightly touching the wall of the beaker when the sample is taken out), grinding the sample into powder by using an agate mortar, dividing the powder into equal parts, placing the equal parts in a magnetic boat, placing the equal parts on two sides of the central axis of a BTF-1200C type tubular vacuum furnace (the sample is prevented from being burnt in the calcination process so as to cause experimental failure), and carrying out high-temperature calcination, wherein the relevant parameters of the tubular furnace are as follows: calcining at 550 ℃, heating up at 5 ℃/min, and calcining at constant temperature for 4 hours. And cooling to below 100 ℃ after the calcination of the vacuum tube furnace is completed, taking out the sample, grinding the sample into powder, and filling the powder into a small-size sealing bag for standby.
Bi-g-C is synthesized by doping bismuth nitrate with single component 3 N 4 And repeating the experimental operation steps in the development process of the composite photocatalytic degradation material.
2.3 preparation of the photocatalyst co-doped with the bimetallic element g-C3N4
When the double metal elements samarium and bismuth are doped together with g-C 3 N 4 When synthesizing the composite photocatalyst material, ten groups of 6g urea and 4g melamine are weighed, and then m [ Sm (NO) 3 ) 3 ]:m[Bi(NO 3 ) 3 ](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, 0.4:1.0) and finally mixing ten groups of pre-weighed mixtures of urea and melamine into ten groups of samarium-bismuth mixtures respectively, wherein the rest experimental operation steps are the same as 2.2.
Structural characterization of the second part, composite photocatalyst
Adopting XRD (X-ray diffraction) by taking Cu K alpha as a radiation source, and carrying out characterization on the crystal phase structure of the sample under the conditions of a scanning speed of 0.1sec/step and a scanning range of 10-80 DEG; and FT-IR is used in the scanning range of 4000-500cm -1 Precision of 0.0001cm -1 The catalyst was analyzed for its material structure and intermolecular interactions at a rate of 32 times/min.
1. X-ray diffraction (XRD) analysis
To further study the introduction of the bimetal element samarium and bismuth to g-C 3 N 4 Action of basic Crystal Structure, photocatalyst g-C 3 N 4 、g-C 3 N 4 -Sm、g-C 3 N 4 -Bi、g-C 3 N 4 XRD spectrum analysis was performed on samples of Sm-Bi, etc., as shown in FIGS. 1a and 1 b.
As can be seen from FIG. 1a, the pure group g-C 3 N 4 The crystal structure of (2) shows characteristic peaks at 13.1 ° and 27.5 °. The relatively weak peak is at 13.1 deg. due to the (100) plane peak, g-C 3 N 4 Diffraction peaks of intra-layer hole spacing formed by carbon and nitrogen six-membered ring 3-s triazine structural units in planar two-dimensional frame, and strong peaks are attributed to g-C 3 N 4 The (002) crystal face peak of (C) is g-C 3 N 4 Lamellar interlayer-characteristic diffraction peaks. And photocatalyst sample g-C doped with metal element 3 N 4 -Sm、g-C 3 N 4 -Bi and g-C 3 N 4 Sm-Bi also showed both typical diffraction peaks, with each set of catalyst samples forming a strong diffraction peak near the 27.5 ° position and a weak or almost vanishing peak at about 13.1 °. With pure g-C 3 N 4 Sample carefulAs can be seen by comparison, the metal doped photocatalyst changes the peak intensity of the characteristic diffraction peak to some extent (see FIG. 1 b), wherein the catalyst samples g-C 3 N 4 Sm-Bi has the weakest characteristic diffraction peak intensity at 27.5 DEG, g-C 3 N 4 Sm times, g-C 3 N 4 Bi is again, pure g-C 3 N 4 The peak intensity of (2) is highest.
g-C prepared by co-doping of bimetallic elements 3 N 4 The Sm-Bi has reduced peak intensity at 27.5 DEG and the peak at 13.1 DEG disappears, which indicates that samarium and bismuth atoms are uniformly embedded in the polymer skeleton, i.e. Sm/Bi/g-C is successfully prepared 3 N 4 A composite photocatalyst material. g-C 3 N 4 The characteristic peak intensities of Sm-Bi located near 13.1 DEG and 27.5 DEG are reduced, which is influenced by the co-doping of the double metal elements samarium bismuth 3 N 4 Resulting from a complete polymerization reaction under high temperature conditions. The photocatalytic material g-C synthesized by bimetallic co-doping was not observed in comparison with the general peak shape and peak position of pure component graphite phase carbon nitride even though the characteristic peak intensity was lowered 3 N 4 Significant changes in the diffraction peak orientation of Sm-Bi indicate that doped g-C can also be formed in the presence of metal ions 3 N 4 The basic structure does not need to change the original graphite-like basic skeleton of the carbonitride, so that the doping of metal elements does not change g-C 3 N 4 The arrangement structure of the basic crystal forms only can change some structural fragments slightly, and the weak structural change does not affect the number of photocatalytic reaction active sites of the carbon nitride, and at the same time, the photocatalytic degradation capability of the carbon nitride is not weakened. That is, sm and Bi are introduced into g-C on two-dimensional plane 3 N 4 The crystal structure and photocatalytic activity of the ligand have no negative effect.
2. Fourier infrared spectroscopy (FT-IR) analysis
As can be seen from FIG. 2, at 820cm -1 And 1250-1700cm -1 Vibration peaks appear in the regions of (2) and are respectively compared with the vibration peak ranges caused by breathing vibration and stretching vibration of the carbon-nitrogen six-membered ring, which indicates that four groups of catalyst samplesA carbon nitrogen triazine heterocyclic skeleton vibration peak unique to graphite phase carbon nitride appears. And at 3150-3350cm -1 The left and right vibration peaks are caused by-OH and-NH stretching vibration, and are respectively derived from water molecules adsorbed by the sample and unpolymerized amine groups on the surface of the catalyst sample. Sample g-C 3 N 4 -Sm、g-C 3 N 4 -Sm-Bi at 2200cm -1 The vibration peak occurring in the vicinity is attributed to the telescoping vibration of azide, and the vibration peak increases with co-doping of Sm and Bi, and it is shown that Sm-Bi chemical bonds may be formed by co-doping of Sm and Bi. In addition, it can be seen from comparing FT-IR spectra of four groups of catalyst samples, except at 2200cm -1 Apart from the difference between the nearby vibration peaks, single metal doped or double metal co-doped g-C 3 N 4 Prepared catalyst and pure component g-C 3 N 4 The FT-IR spectrum of the catalyst was substantially unchanged at 1900cm -1 The absorption peak intensity at the location varies only slightly. This shows that the co-doping of the double metals Sm and Bi does not significantly change the g-C 3 N 4 The Sm and Bi co-doping can effectively strengthen the photodegradation performance of the catalyst on dye pollutants and still maintain g-C 3 N 4 Chemical structure advantages of (a).
Third part, monomer g-C 3 N 4 Samarium doped g-C 3 N 4 Bismuth doped g-C 3 N 4 Co-doping of bimetal element g-C 3 N 4 Photocatalytic Property study of materials
The degradation performance of the catalyst sample on dye contaminants was determined using a self-made photocatalytic degradation simulation test apparatus as shown in fig. 3, and the detailed test procedure was to weigh 10mg of the photocatalyst sample into (50 mL, 0.02 g/L) Methylene Blue (MB) aqueous solution using an analytical balance, and place the mixture suspension in a black-painted environment for magnetically stirring for 30min before turning on the xenon lamp 1 to saturate the adsorption-desorption state between the photocatalyst sample and the MB aqueous solution. Then continuing to stir the reaction solution 2 by using magnetic stirring, simultaneously turning on the xenon lamp 1 to continuously irradiate for 90min, taking 4mL of the reaction solution by using a pipette every 15min, and placing the reaction solution in a containerCentrifuge tubes and number for further use. After the photocatalytic degradation experiment is completed, a low-rotation-speed desk-top centrifuge is used for further photocatalytic performance evaluation, and the rotation speed is set to 3000 r.min- 1 Centrifuging the sampled solution for 1min to precipitate photocatalyst particles suspended in MB solution, sucking the upper layer impurity-free solution through a rubber head dropper, and measuring the absorbance of the residual MB solution after photodegradation at 664nm by using a TU-1901 model single-beam visible spectrophotometer.
1. Statistical method
The initial concentration of MB is marked as Co, the MB concentration sampled at the time t is marked as C, the photocatalytic degradation rate C/Co is used as y coordinate axis to make a line graph for the reaction time t, and the line graph can effectively and intuitively reflect the metal modified doping g-C in the system 3 N 4 The prepared composite photocatalyst simulates degradation of dye pollutant MB. Wherein the percent degradation of the simulated contaminant MB solution can be calculated by the following mathematical formula:
2. g-C prepared from different starting materials 3 N 4 Photocatalytic Activity
As shown in Table 3, g-C was prepared from melamine and urea as basic raw materials 3 N 4 . The method comprises the steps of respectively selecting basic raw materials of 20 percent of melamine, 40 percent of melamine, 50 percent of melamine, 60 percent of melamine and 80 percent of melamine when 10g of 100 percent of melamine, 10g of 100 percent of urea and the sum of the mass of urea and melamine is 10g, preparing a graphite phase carbon nitride photocatalyst of pure components, and calcining at a high temperature of 550 ℃ in a vacuum tube furnace. As shown in table 4:
TABLE 4 Table 4
After repeated experimental determination of photocatalytic degradation 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 in the photocatalytic degradation process, a line graph of the degradation rate of the simulated pollutant MB solution converted with time by the specific catalyst is shown in fig. 4.
The experimental data above indicate that:
(1) preparation of g-C from pure melamine 3 N 4 The highest yield but the lowest photocatalytic degradation rate was only 38.41%.
(2) Preparation of g-C from pure urea 3 N 4 The photocatalytic degradation rate of (2) was 52.11% which is next to the highest 40% ratio of melamine component to yield 61.43%, however, pure urea produced g-C 3 N 4 The yield of (2) is at least 5.83% of the above-mentioned raw materials for preparing carbon nitride, which is caused by the carbonization of urea during the high-temperature calcination and the release of a large amount of ammonia and carbon dioxide which are liable to volatilize, but when melamine is mixed with urea in proportion to prepare g-C 3 N 4 On the one hand, the addition of urea increases the g-C produced 3 N 4 Specific surface area, modified pure melamine for preparing g-C 3 N 4 Undesirable photocatalysis effect, on the other hand, melamine modified pure urea is used for preparing g-C 3 N 4 The defect of extremely low yield is that the two basic raw materials are mixed in proportion to achieve the best effect.
(3) The addition of urea increases the degradation rate of the photocatalyst and decreases the yield, because the g-C is calcined at high temperature 3 N 4 Urea forms a large amount of carbonic anhydride and ammonia when decomposed by heat at high temperature, since these gases are in g-C 3 N 4 The thermal polymerization proceeds in the form of small bubbles, causing the carbon nitride to form a loose porous structure, and g-C as the urea doping content increases 3 N 4 The 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 widened 3 N 4 Receiving area for visible light, thereby improving g-C 3 N 4 Is used for the photocatalytic degradation activity of (a).
(4) Melamine content 20%, 50%, 80%, 60% of the components of the composition 3 N 4 With the addition of urea in successive amounts, the degradation rate of the catalyst is slowly increased, but at the same time g-C 3 N 4 The yield of (2) decreases with a gradual decrease in the melamine ratio.
(5) The g-C is prepared by 40 percent of components of melamine (namely, m urea: m melamine is 6:4) 3 N 4 The photocatalytic degradation rate of the catalyst is 61.43 percent which is highest, and the catalyst yield reaches 31.02 percent, namely the optimal proportioning state of the melamine and urea after mixing is achieved. Finally, the preparation of g-C by mixing urea melamine in a mass ratio of 6:4 is finally determined 3 N 4 Is a basic raw material of (a) a powder.
3. Photocatalytic activity of Sm doped with g-C3N4 with different doping amounts
On the one hand explores the effective modification of rare earth element samarium g-C 3 N 4 Mechanism of photocatalytic performance; on the other hand, the method is used for deeply researching the synthetic photocatalyst g-C with the metal element samarium 3 N 4 Optimum doping mass ratio of Sm (X), wherein X is taken (1% -10%), ten groups of g-C are prepared in total by the experimental procedure of the above synthetic photocatalytic material 3 N 4 Sm (X) material, as shown in fig. 5, is a plot of the degradation rate of a portion of the material versus time for a simulated contaminant methylene blue solution (MB).
As can be seen from the photocatalytic degradation results shown in FIG. 5, when X (X is the mass content of samarium) is less than 4%, g-C 3 N 4 The photocatalytic degradation effect of Sm (X) sample on MB increases in gradient with further increase of the doping amount X of the metal Sm, and g-C when X takes 4% 3 N 4 Sm (4%) had the best degradation effect on methylene blue MB solution, and the removal efficiency of MB solution increased to 81.96% of the line graph peak. But when the value of X is higher than 4%, g-C 3 N 4 The photocatalytic function of the Sm (X) sample on MB is reduced in a gradient manner with further increase of the doping amount X of the metal Sm. I.e. the excess rare earth element Sm is doped with g-C 3 N 4 Degradation of MB by the photocatalyst is adversely affected due to recombination of the excess rare earth element Sm with the centers of electrons and holes, promotion of recombination of photogenerated carriers, resulting in lightCatalyst g-C 3 N 4 -Sm (5% -10%) reduced photocatalytic degradation rate of MB solution.
Furthermore, as can be seen from FIG. 5, pure g-C 3 N 4 The photocatalytic degradation of MB is the worst, and g-C 3 N 4 -Sm (4%) has a photocatalytic degradation rate of 1.3 times that of Sm. Thus, the photocatalytic experimental results in this section show that: (1) rare earth element samarium doped g-C 3 N 4 Synthesized g-C 3 N 4 Sm photocatalyst can effectively modify g-C 3 N 4 The defects of the catalyst and greatly improve the photocatalytic degradation activity of the catalyst; (2) rare earth element samarium doped g-C 3 N 4 Synthetic photocatalytic sample g-C 3 N 4 The optimum amount of Sm to be incorporated is 4%, i.e. g-C 3 N 4 Sm (4%) has the best photocatalytic effect and has a more ideal photocatalytic degradation effect compared with pure g-C3N 4.
From the photocatalytic results reflected in FIG. 5, it was found that g-C was obtained by analysis in combination with XRD patterns 3 N 4 Sm has a mesoporous structure inside, which is comparable to the g-C in bulk 3 N 4 With a large difference. Multiple refraction and scattering are caused when visible light strikes the catalyst surface. This porous structure will also make the adsorption and profile Zhang Guocheng of the residual dye small particles more efficient, helping the photocatalytic degradation process. And the mesoporous structure and the original monomer g-C with smooth two-dimensional layered structure 3 N 4 The porous arrangement has more exposed geometric surface in comparison to the structure. I.e. promote g-C 3 N 4 Sm to catalyst ratio g-C 3 N 4 Has more active sites and can effectively promote the photocatalysis reaction speed of the material.
4. Co-doping Bi with different doping amounts and 4% Sm to prepare g-C 3 N 4 Photocatalytic Activity
Ten groups of samarium bismuth bimetal co-doped g-C are prepared in the section 3 N 4 Prepared g-C 3 N 4 -Sm (4%) -Bi (Y) (Y takes a value of 1% -10%) composite photocatalyst samples, and ten groups of photocatalyst samples were tested for their degradation activity on MB solution, and specific photocatalytic results are shown in fig. 3-5. At the position ofSingle component samarium doped g-C 3 N 4 On the basis of preparing the photocatalyst, the addition of the metal element bismuth strengthens the g-C 3 N 4 The degradation effect of the material on MB. When catalyst sample g-C 3 N 4 When the value of Y (Y is the mass content of Bi) in Sm (4 percent) -Bi (Y) is 1 to 4 percent, the degradation rate of the sample catalyst to the analog dye waste MB gradually increases along with the increase of the doping amount of the metal bismuth (the photocatalytic degradation rate is 81.95 percent, 65.38 percent, 78.39 percent, 82.66 percent and 87.39 percent in sequence). When the doping amount of the metal element bismuth is 4%, the removal rate of MB by the photocatalyst sample reaches 87.39% of the peak value, compared with the photocatalyst g-C 3 N 4 The degradation rate of Sm (4%) was 81.96% higher than that of the photocatalyst sample g-C by about 5.43% 3 N 4 When Y in Sm (4%) -Bi (Y) takes a value of 5% -10%, the degradation rate of the catalyst to MB gradually decreases 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).
It was found that the doping amount of metallic bismuth can change the degradation effect of the photocatalyst, and that moderate metallic bismuth doping can significantly enhance g-C 3 N 4 The photodegradation of MB solution. However, excessive bismuth doping can run counter to the desired effect. This may be an excessive doping of metallic bismuth blocking the g-C 3 N 4 The mesoporous structure of Sm causes a decrease in the absorption efficiency of the prepared photocatalyst for visible light, thus causing a significant impairment of the degradation activity of the catalyst for MB solutions. Therefore, the experimental result shows that the rare earth element samarium is doped with g-C in a single component 3 N 4 On the basis of the above, the addition of the metal bismuth remarkably improves the light removal rate of the material on the simulated organic pollutant MB. And, bimetal co-doping g-C 3 N 4 Preparation of composite photocatalyst g-C 3 N 4 The optimum doping amount of metallic bismuth in Sm-Bi was 4%, sample g-C 3 N 4 -Sm (4%) -Bi (4%) with photocatalytic degradation rate as high as 87.39% pure g-C 3 N 4 1.5 times of the photocatalyst.
5. First order kinetic fitting of chemical reactions
As shown in FIG. 7a, four groups of photocatalysts g-C are compared 3 N 4 、g-C 3 N 4 -Bi(4％)、g-C 3 N 4 -Sm(4％)、g-C 3 N 4 Sm (4%) -Bi (4%) photocatalytic degradation of MB solution within 2h, from which it can be seen that the bimetallic co-doping g-C 3 N 4 Prepared g-C 3 N 4 The photocatalytic degradation effect of the Sm (4 percent) -Bi (4 percent) catalyst is optimal, and the photocatalytic degradation rates are respectively pure g-C 3 N 4 、g-C 3 N 4 -Bi(4％)、g-C 3 N 4 1.42 times, 1.37 times, 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 MB, a chemical first-order dynamics fitting curve of the photocatalytic degradation process of the MB solution by the four groups of samples is further drawn.
When the concentration of MB is low, its function of concentration over time during the course of decomposition is consistent with the law of the quasi-first order reaction kinetics simulation curve, so that 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 from undoped metal elements 3 N 4 The photocatalytic degradation reaction rate constant is the lowest, and samarium and bismuth are doped with g-C as a single component 3 N 4 Prepared g-C 3 N 4 -Sm(4％)、g-C 3 N 4 The reaction rate constant of Bi (4%) is significantly higher than that of pure g-C 3 N 4 This shows that the single metal element samarium, bismuth, was successfully doped in g-C 3 N 4 In (3), and effectively strengthen g-C 3 N 4 On the other hand, the bimetallic samarium bismuth is co-doped with g-C 3 N 4 Prepared composite photocatalytic material g-C 3 N 4 -Sm (4%) -Bi (4%) has a photocatalytic reaction rate constant of up to 0.02362h -1 Specific purity g-C 3 N 4 Higher than 0.01311h -1 At the same time dope g-C with metal than single component 3 N 4 Synthetic material g-C 3 N 4 -Bi (4%) higher than 0.01300h -1 Ratio g-C 3 N 4 Sm (4%) is higher than 0.00483h -1 Left and right. Thus, the above experimental data fully demonstrate g-C 3 N 4 Sm (4%) -Bi (4%) greatly increases g-C 3 N 4 Is used for the photocatalytic degradation efficiency of the polymer.
6. Calcination temperature vs. catalyst g-C 3 N 4 Effect of photocatalytic Activity of Sm-Bi
FIGS. 8a and 8b show the catalyst samples g-C at different calcination temperatures for a calcination time of 4 hours 3 N 4 -Sm
(4%) -Bi (4%) line graph of MB-degrading solution. As is clear from the graph, the calcination time was controlled to be constant for 4 hours, the photocatalytic degradation effect on MB was relatively excellent when the calcination temperature was 550 ℃, and the photocatalytic degradation rate of the catalyst was increased in a gradient manner when the calcination temperature was increased from 530 ℃ to 550 ℃, but the photocatalytic degradation rate of the catalyst was gradually decreased in a gradient manner when the calcination temperature was increased from 550 ℃ to 580 ℃. This means that 550℃is both peak and limiting, i.e. less than 550℃with an increase in temperature, the catalyst produced has a greater photocatalytic performance, whereas above 550℃it is vice versa. Therefore, when the calcination time is constant and the calcination temperature is 550 ℃, the calcination effect of the photocatalyst is optimal.
7. Calcination time vs g-C 3 N 4 Effect of photocatalytic Activity of Sm-Bi
FIGS. 9a and 9b show different calcination times at 550℃for catalyst samples g-C 3 N 4 -Sm (4%) -Bi (4%) line graph of the MB solution degradation. As can be seen from the figure, the calcination temperature was kept uniform, the degradation effect of the catalyst on MB was best when the calcination time was 3h, and the photocatalytic degradation rate of the catalyst was increased in a gradient manner when the calcination time was prolonged from 1h to 3h, but the photocatalytic degradation rate of the catalyst was gradually decreased in a gradient manner when the calcination temperature was prolonged from 3h to 6 h. When the calcination temperature is relatively low or the calcination time is short, the crystallinity of the photocatalyst is relatively small, and the photo-generated electrons and holes are easy to recombine, namely the photocatalytic activity is deviated; and when the calcination temperature is higher or the calcination time is longer,the particle diameter of the photocatalytic material increases, and the catalyst active sites are cut down, resulting in a decrease in the photocatalytic effect. Thus, the above experimental data show that when the tube furnace calcination temperature was set to 550℃and the calcination time was set to 3 hours, the bimetal co-doped g-C 3 N 4 Prepared g-C 3 N 4 The degradation rate of the Sm-Bi composite photocatalyst is most ideal and reaches as high as 90.34 percent.
Third part, conclusion
Pure g-C 3 N 4 Based on the structural characteristics of bare carbon nitride, the specific surface area is low, the photo-generated-electron recombination rate is high, and the utilization rate of visible light is low, so that the photocatalytic degradation activity of the carbon nitride is limited [33] . In this case, the co-doping of the bimetallic element Sm and Bi can effectively overcome the g-C 3 N 4 Is a major obstacle to such disorders. The bimetallic Sm and Bi co-doped 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 method 3 N 4 The photocatalyst g-C3N4-Sm-Bi.
(1) The best mixing ratio of melamine and urea and Sm and Bi single-component metal doping g-C are explored 3 N 4 Co-doping of bimetal g-C 3 N 4 The effect of the optimum incorporation quality, calcination temperature, calcination time on the catalyst photodegradation mimic contaminant activity. Experimental results show that when the calcination temperature is 550 ℃, the calcination time is 3 hours, the mass ratio of urea to melamine is 6:4, and the mass ratio of Sm to Bi codoping is 4:4%, the photocatalysis effect is optimal, and the prepared photocatalyst g-C 3 N 4 Sm (4%) -Bi (4%) MB (10 mg/L) was irradiated for 90min after continuous irradiation -1 ) The degradation rate of (a) reaches 90.34 percent, and is pure g-C 3 N 4 1.5 times of (2).
(2) As can be seen from the results of spectrum characterization such as XRD, FT-IR and the like, the co-doping of the bimetal Sm and Bi does not change g-C 3 N 4 But does reduce g-C 3 N 4 The specific surface area of the catalyst is increased, the recombination of photo-generated charge carriers is inhibited, and the simulation of the photocatalyst to an organic pollutant MB solution is further enhancedDegradation properties.
In summary, the structural characterization and photocatalytic performance evaluation of the combined catalyst prove that the g-C with good stability and excellent photocatalytic degradation activity is synthesized by a simple calcination method 3 N 4 -Sm (4%) -Bi (4%) photocatalyst.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While the obvious variations or modifications which are extended therefrom remain within the scope of the claims of this patent application.
Claims (5)
1. The preparation method of the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material is characterized by comprising the following steps:
(1) Mixing melamine and/or urea with a mixture of a soluble samarium salt and a soluble bismuth salt, and then dissolving in deionized water under magnetic stirring at room temperature; in step (1): the sum of the mass 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; the soluble samarium salt is samarium nitrate, and the soluble bismuth salt is bismuth nitrate; the mass ratio of samarium nitrate to bismuth nitrate is 0.4: (0.1-1.0);
dissolving a mixture of melamine and/or urea and a mixture of a soluble samarium salt and a soluble bismuth salt in a beaker filled with 60mL of deionized distilled water, then placing the mixture on a constant-temperature magnetomotive electric stirrer, stirring the mixture for 30 minutes at room temperature, and fully and uniformly mixing the components;
(2) Heating to dry by stirring, and solidifying;
(3) Then placing the mixture in an oven for drying, cooling and grinding the mixture into powder;
(4) Placing the powder sample in a tubular vacuum furnace, calcining at high temperature, cooling, and grinding into powder to obtain bimetal elementSamarium and bismuth co-doped g-C 3 N 4 Synthesizing the composite photocatalyst material.
2. The method for preparing a Bi-metal Sm, bi co-doped graphite-phase carbon nitride composite photocatalyst material according to claim 1, characterized in that in the step (2), the temperature of a constant temperature heating magnetic stirrer is adjusted to 80 ℃, and the mixture is stirred and heated at a constant temperature until all water is evaporated to dryness, and the whole is in a solidified state.
3. The method for preparing a Bi-metal Sm, bi co-doped graphite phase carbon nitride composite photocatalyst material according to claim 1, characterized in that in step (3), the beaker in step (2) is placed in an oven with a temperature adjusted to 100 ℃ to be dried, after 4 hours, the dried and agglomerated sample is taken out and ground into powder by using an agate mortar.
4. The method for preparing the bimetallic Sm and Bi co-doped graphite phase carbon nitride composite photocatalyst material according to claim 1, wherein in the step (4), the calcination parameters of the tubular vacuum furnace are as follows: calcining at 550 ℃ at a temperature rising speed of 5 ℃/min for 4 hours at constant temperature; cooling to below 100deg.C after calcining in vacuum tube furnace, taking out sample, grinding into powder to obtain bimetal element samarium and bismuth doped g-C 3 N 4 Synthesizing the composite photocatalyst material.
5. The photocatalytic degradation application of the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material prepared according to any one of claims 1 to 4, wherein the Bi-metal Sm and Bi co-doped graphite-phase carbon nitride composite photocatalyst material can perform photocatalytic degradation on methylene blue under a photocatalytic condition.
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