CN117563652A - Preparation of mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater - Google Patents
Preparation of mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater Download PDFInfo
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- 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
- C02F1/72—Treatment of water, waste water, or sewage by oxidation
- C02F1/725—Treatment of water, waste water, or sewage by oxidation by catalytic oxidation
-
- 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
-
- 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
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
- B01J37/0027—Powdering
- B01J37/0036—Grinding
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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
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/08—Heat treatment
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/08—Heat treatment
- B01J37/10—Heat treatment in the presence of water, e.g. steam
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- 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
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
- C22B60/02—Obtaining thorium, uranium, or other actinides
- C22B60/0204—Obtaining thorium, uranium, or other actinides obtaining uranium
- C22B60/0217—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes
- C22B60/0252—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes treatment or purification of solutions or of liquors or of slurries
- C22B60/0278—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes treatment or purification of solutions or of liquors or of slurries by chemical methods
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/006—Radioactive compounds
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/08—Seawater, e.g. for desalination
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Abstract
The invention relates to a preparation method of a mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater, which comprises the following steps: synthesizing mesoporous carbon nitride by a hard template method; building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst: ultrasonically dispersing mesoporous carbon nitride in deionized water to obtain mesoporous carbon nitride suspension with the solid content of 1-2%; glucose and cadmium nitrate are sequentially added into the mesoporous carbon nitride suspension, stirring is carried out, thioglycollic acid is added, continuous stirring is carried out for 1h, hydrothermal reaction is carried out, and the obtained reaction product is washed and freeze-dried, so that the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with the cadmium sulfide load of 5-50% is obtained. The composite photocatalyst obtained by the invention can realize high-efficiency and rapid extraction of U (VI) in seawater, and the composite catalyst still maintains high stability, high catalytic reaction activity and good recycling performance after elution and recovery.
Description
Technical Field
The invention relates to the technical field of photocatalysis seawater uranium extraction materials, in particular to preparation of a mesoporous carbon nitride/cadmium sulfide catalyst for seawater uranium extraction.
Background
The nuclear energy has the advantages of low operation cost, safety, reliability, near zero carbon emission and the like, and occupies an indispensable important position in a green low-carbon energy system in China. As a clean and efficient energy source, nuclear energy provides 10% of the global electricity, can help to reduce emissions of about 200 billion tons of carbon dioxide each year, and is of great significance in achieving the "zero carbon" goal. Uranium (U) is used as a 'strong nuclear foundation stone, a nuclear power granary', and development and safe supply of the uranium (U) are critical for long-term sustainable development of nuclear energy. However, land uranium resources are extremely limited, and land uranium reserves of about 500 ten thousand tons have been ascertained, and according to the current consumption rate, only human use can be maintained for 80 to 120 years, and it is difficult to meet the development demands of nuclear energy in the future. Therefore, other unconventional uranium resources are actively developed, and reliable resource guarantee can be provided for the long-term development of nuclear energy in China. The ocean is the biggest uranium resource treasury in the world, the total reserve capacity is up to 45 hundred million tons, which is approximately 1000 times of the established land uranium reserve capacity, and a huge potential fuel source is provided for nuclear energy development. Therefore, in order to ensure the continuous supply of nuclear energy and meet the requirement of human beings on energy, the technology for extracting uranium from seawater and developing seawater uranium extraction has important strategic significance for ensuring the sustainable development of nuclear energy.
Heretofore, conventional methods for separating enriched uranium from seawater mainly include ion exchange, extraction, membrane separation, chemical reduction, adsorption, and the like. Because of low uranium concentration, high salinity and complex components in seawater, the traditional seawater uranium extraction technology faces a plurality of challenges, and the development of a novel and efficient seawater uranium extraction technology is particularly important. The photocatalysis method can directly utilize sunlight to efficiently and selectively drive U (VI) to be reduced without applying external driving force, so that the reaction is more economical, convenient and sustainable, an innovative technical strategy is provided for extracting uranium from seawater, and the photocatalysis method has wide application prospect. For example, a photo-thermal photocatalysis film for sea water desalination-uranium extraction co-production and preparation method thereof (CN 114931862B), a high-dispersivity C 3 N 4 The content is related to a sea water uranium extraction composite material and a preparation method thereof (CN 115228500A), a sea water uranium extraction amidoxime group cyclized polyacrylonitrile material preparation method (CN 202210754446.8), a sea water desalination-uranium extraction co-production semiconductor photoreduction membrane and a preparation method thereof (CN 202210598986.1), a preparation method of an ethylenediamine coated cadmium telluride nano-belt photocatalyst, a separation method of uranium in radioactive wastewater (CN 202110245812), a photocatalytic uranium capture two-dimensional sheet semiconductor and a preparation method thereof (CN 202210754425), a preparation and application of a uranium reduction separated Ag doped CdSe nano-sheet photocatalytic material (CN 202110775914), a preparation and application of a mesoporous titanium dioxide photocatalyst for photocatalytic uranium reduction (CN 202211301548) and the like.
The core of the technology for separating enriched uranium from seawater by photocatalysis is a photocatalyst, so that the development of an economic, efficient and stable photocatalyst has important practical significance for the application and expansion of photocatalysis of seawater uranium extraction. Graphite phase carbon nitride has excellent physicochemical stability, energy band adjustability, morphological diversity and typical nonmetallic characteristics, and has attracted great attention in the field of photocatalytic reduction. However, carbon nitride obtained by direct thermal polymerization has disadvantages of relatively low specific surface area, few intrinsic active sites, serious recombination of photogenerated electrons and holes, and the like, and has limited light absorption performance and serious carrier recombination, resulting in low photocatalytic reduction efficiency for U (VI) and low quantum efficiency in the visible region. Meanwhile, in most systems, the photocatalytic reduction of U (VI) is severely inhibited in an air atmosphere, which greatly limits the practical application of the photocatalytic method.
Disclosure of Invention
The invention aims to provide an efficient and economical preparation method of a mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater.
In order to solve the problems, the preparation method of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater comprises the following steps:
synthesizing mesoporous carbon nitride by a hard template method:
by reacting cyanamide with SiO 2 Uniformly mixing the nanoparticle dispersion liquid to obtain a mixture A, stirring the mixture A at 70-80 ℃ for reaction for 8-12 h, calcining the obtained reaction product for 4h at 550 ℃ in argon atmosphere, cooling and grinding to obtain a calcined product; dispersing the calcined product in 3-4M hydrogen fluoride ammonia water solution, stirring and reacting for 24 hours, washing, and vacuum freeze-drying for 12 hours to obtain mesoporous carbon nitride;
building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst:
ultrasonically dispersing the mesoporous carbon nitride in deionized water to obtain a mesoporous carbon nitride suspension with the solid content of 1-2%; glucose and cadmium nitrate (Cd (NO) 3 ) 2 ·4H 2 O) and stirring for 4 hours, adding thioglycollic acid (TGA), and stirring for 1 hour to obtain a mixture B; carrying out hydrothermal reaction on the mixture B for 2 hours at 170-190 ℃, washing the obtained reaction product by absolute ethyl alcohol, and freeze-drying to obtain the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with 5-50% of cadmium sulfide loading; the mesoporous carbon nitride: glucose: the mass ratio of thioglycollic acid is 1:2:6.
the steps include 2 SiO in nanoparticle dispersion 2 The particle size of the nano particles is 11-13 nm, and the mass concentration is 35-45%.
In the step (A), the mass concentration of the cyanamide in the mixture A is 8-12%.
The steps include 2 The mass ratio is 1.0:0.1 to 1.0:0.8.
the calcining heating rate is controlled to be 2-3 ℃/min in the step.
The mass volume ratio of the calcination product to the hydrogen fluoride ammonia solution in the step (A) is 1:20.
the freeze drying condition in the step is that the temperature is-50 ℃ and the time is 12-24 hours.
Compared with the prior art, the invention has the following advantages:
1. according to the invention, mesoporous carbon nitride is introduced, so that the visible light absorption and the photo-generated carrier separation efficiency are greatly improved, the photo-catalytic reduction efficiency of U (VI) is remarkably enhanced, and good reaction selectivity is still shown for U (VI) when coexisting ions exist; the method further comprises the step of constructing a composite catalyst by coupling the catalyst with a narrow-band-gap cadmium sulfide semiconductor, and keeping ideal photocatalytic reduction efficiency for U (VI) in the air, natural light and seawater under the condition of no adding of a sacrificial agent, so that the method is expected to realize large-scale separation, enrichment and high-value utilization of uranium resources in the seawater by the aid of the practical application of a boosting photocatalytic uranium extraction technology under multiple systems and working conditions.
2. Under the irradiation of visible light, the extraction capacity of the mesoporous carbon nitride/cadmium sulfide composite photocatalyst prepared by the invention to U (VI) can reach 2379-2770 mg/g, and the photocatalytic reduction efficiency is about 7-10 times of that of single component of carbon nitride or cadmium sulfide; under the condition of no sacrificial agent, the compound photocatalyst can completely reduce U (VI) in a system within 6 min, and the reaction rate is up to 0.656 min −1 。
3. The composite photocatalyst obtained by the invention can realize high-efficiency and rapid extraction of U (VI) in seawater, and the composite catalyst still maintains high stability, high catalytic reaction activity and good recycling performance after elution and recovery.
4. The invention selects stable, cheap and easily available graphite phase carbon nitride and cadmium sulfide as basic materials, and adopts systematic research and preparation processOptimizing, successfully developing heterogeneous photocatalyst with excellent performance, directly utilizing sunlight to efficiently and selectively drive U (VI) to be reduced and fixed, realizing separation and extraction of uranium in seawater and hardly releasing Cd to environment 2+ Solves the problems of low photocatalytic reduction efficiency, easy inhibition and the like existing in the photocatalytic seawater uranium extraction, provides a green and efficient new way for the development of the seawater uranium extraction technology, and has good industrial application prospect and social benefit.
Drawings
The following describes the embodiments of the present invention in further detail with reference to the drawings.
FIG. 1 is an XRD spectrum of mesoporous carbon nitride (left) and mesoporous carbon nitride/cadmium sulfide composite photocatalyst (right) prepared by the present invention.
FIG. 2 is a TEM image of cadmium sulfide (left), mesoporous carbon nitride (middle) and mesoporous carbon nitride/cadmium sulfide composite photocatalyst (right) prepared according to the present invention.
FIG. 3 is a graph showing the change of the removal rate of the photocatalytic reduction of U (VI) by the mesoporous carbon nitride/cadmium sulfide composite photocatalyst prepared by the invention.
FIG. 4 is a graph showing the change of the removal rate of the mesoporous carbon nitride/cadmium sulfide composite photocatalyst prepared by the invention in the photocatalytic reduction of U (VI) in the labeled seawater.
FIG. 5 shows Cd in the photocatalytic reduction of U (VI) by using a pure cadmium sulfide and mesoporous carbon nitride/cadmium sulfide composite photocatalyst 2+ Is a release profile of (2).
Detailed Description
The preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater comprises the following steps:
synthesizing mesoporous carbon nitride by a hard template method:
by reacting cyanamide with SiO 2 Uniformly mixing the nanoparticle dispersion liquid to obtain a mixture A, stirring the mixture A at 70-80 ℃ for reaction for 8-12 hours, calcining the obtained reaction product for 4 hours at 550 ℃ in argon atmosphere, controlling the calcining heating rate at 2-3 ℃/min, cooling and grinding to obtain a calcined product; dispersing the calcined product in 3-4M hydrogen fluoride ammonia water solution, stirring and reacting for 24 hours, and carrying out the following stepsWashing and vacuum freeze drying for 12h to obtain the mesoporous carbon nitride.
Wherein: siO (SiO) 2 SiO in nanoparticle dispersion 2 The particle size of the nano particles is 11-13 nm, and the mass concentration is 35-45%. The mass concentration of the cyanamide in the mixture A is 8-12%. Cyanamide and SiO 2 The mass ratio (g/g) is 1.0:0.1 to 1.0:0.8.
the mass volume ratio (g/ml) of the calcined product to the aqueous hydrogen fluoride ammonia solution is 1:20.
building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst:
ultrasonically dispersing mesoporous carbon nitride in deionized water to obtain mesoporous carbon nitride suspension with the solid content of 1-2%; glucose and cadmium nitrate (Cd (NO) 3 ) 2 ·4H 2 O) and stirring for 4h, adding thioglycollic acid (TGA), mesoporous carbon nitride: glucose: the mass ratio of thioglycollic acid is 1:2:6, stirring continuously for 1h to obtain a mixture B; and carrying out hydrothermal reaction on the mixture B for 2 hours at 170-190 ℃, generating cadmium sulfide on the surface of the obtained reaction product, washing the reaction product by absolute ethyl alcohol, and freeze-drying at-50 ℃ for 12-24 hours to obtain the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with 5-50% cadmium sulfide loading.
According to the invention, the catalyst with the cadmium sulfide loading of 5-50% can be prepared by changing the cadmium sulfide proportion (the mass ratio (g/g) of cadmium sulfide to mesoporous carbon nitride is 0.31-3.1).
Example 1 a mesoporous carbon nitride/cadmium sulfide catalyst for uranium extraction from seawater was prepared, comprising the steps of:
synthesizing mesoporous carbon nitride by a hard template method:
into a 250mL round bottom flask was added sequentially 20g of cyanamide and 35.5g of SiO 2 Nanoparticle dispersion (SiO) 2 The particle size of the nano particles is 12nm, the mass concentration is 45 percent), 55.5g of mixture A is obtained after uniform mixing, the mixture A is stirred at 80 ℃ for reaction for 12 hours to remove water, the obtained reaction product is placed in a muffle furnace, the temperature is increased at the heating rate of 2 ℃ per minute under the protection of argon, the mixture is calcined at 550 ℃ for 4 hours, and the mixture A is ground and sieved by a 100-mesh sieve after being naturally cooled to room temperature to obtain 45g of calcined product; the calcined product was dispersed in 200ml of concentrateStirring and reacting in 4M hydrogen fluoride ammonia water solution for 24h to completely remove SiO 2 And washing the template with distilled water and ethanol for 4 times, and finally performing vacuum freeze drying for 12 hours to obtain 10g of mesoporous carbon nitride, wherein the mesoporous carbon nitride is marked as mesoporous carbon nitride-Si-0.8.
Building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst:
2g of mesoporous carbon nitride is ultrasonically dispersed in 200ml of deionized water to obtain mesoporous carbon nitride suspension with 1% of solid content; 4g glucose and 0.62g cadmium nitrate (Cd (NO) 3 ) 2 ·4H 2 O) and stirring for 4h, adding 12g thioglycollic acid (TGA) and stirring for 1h to obtain a mixture B; and carrying out hydrothermal reaction on the mixture B for 2 hours at 190 ℃, washing the obtained reaction product by absolute ethyl alcohol, and freeze-drying at-50 ℃ for 12-24 hours to obtain the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with 5% cadmium sulfide loading, wherein the mesoporous carbon nitride/cadmium sulfide composite photocatalyst is marked as mesoporous carbon nitride/cadmium sulfide-5.
Example 2 preparation of a mesoporous carbon nitride/cadmium sulfide catalyst for uranium extraction from seawater, comprising the following steps:
synthesizing mesoporous carbon nitride by a hard template method:
to a 250mL round bottom flask was added 30 g cyanamide followed by 8.6g SiO 2 Nanoparticle dispersion (SiO) 2 The particle size of the nano particles is 11nm, the mass concentration is 35 percent), 38.6g of mixture A is obtained after uniform mixing, the mixture A is stirred at 70 ℃ for reaction for 12 hours to remove water, the obtained reaction product is placed in a muffle furnace, the temperature is increased at the heating rate of 3 ℃ per minute under the protection of argon, the mixture is calcined at 550 ℃ for 4 hours, and the mixture A is ground and sieved by a 100-mesh sieve after being naturally cooled to room temperature to obtain 32.6g of calcined product; dispersing the calcined product in 200M 3M aqueous ammonia solution of hydrogen fluoride with concentration, stirring and reacting for 24h to completely remove SiO 2 And washing the template with distilled water and ethanol for 4 times, and finally performing vacuum freeze drying for 12 hours to obtain 24g of mesoporous carbon nitride, wherein the mesoporous carbon nitride is marked as mesoporous carbon nitride-Si-0.1.
Building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst:
2g of mesoporous carbon nitride is ultrasonically dispersed in 200ml of deionized water to obtain mesoporous carbon nitride suspension with 1% of solid content; mesoporous carbon nitride suspensionTo the suspension were added 4g of glucose and 2.48g of cadmium nitrate (Cd (NO) 3 ) 2 ·4H 2 O) and stirring for 4h, adding 12g thioglycollic acid (TGA) and stirring for 1h to obtain a mixture B; and carrying out hydrothermal reaction on the mixture B for 2 hours at 170 ℃, washing the obtained reaction product by absolute ethyl alcohol, and freeze-drying at-50 ℃ for 12-24 hours to obtain the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with 20% cadmium sulfide loading, wherein the mesoporous carbon nitride/cadmium sulfide composite photocatalyst is marked as mesoporous carbon nitride/cadmium sulfide-20.
Example 3 preparation of a mesoporous carbon nitride/cadmium sulfide catalyst for uranium extraction from seawater, comprising the following steps:
synthesizing mesoporous carbon nitride by a hard template method:
to a 250mL round bottom flask was added 25g cyanamide and 25g SiO sequentially 2 Nanoparticle dispersion (SiO) 2 The particle size of the nano particles is 11nm, the mass concentration is 40 percent), 50g of mixture A is obtained after uniform mixing, the mixture A is stirred at 80 ℃ for reaction for 12 hours to remove water, the obtained reaction product is placed in a muffle furnace, the temperature is increased at the heating rate of 2 ℃ per minute under the protection of argon, the mixture is calcined at 550 ℃ for 4 hours, and the mixture A is ground and sieved by a 100-mesh sieve after being naturally cooled to room temperature to obtain 45g of calcined product; the calcined product was dispersed in 200ml of 4M aqueous hydrogen fluoride ammonia solution and stirred for reaction for 24 hours to completely remove SiO 2 And washing the template with distilled water and ethanol for 4 times, and finally performing vacuum freeze drying for 12 hours to obtain 20g of mesoporous carbon nitride, wherein the mesoporous carbon nitride is marked as mesoporous carbon nitride-Si-0.4.
Building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst:
2g of mesoporous carbon nitride is ultrasonically dispersed in 200ml of deionized water to obtain mesoporous carbon nitride suspension with 1% of solid content; 4g glucose and 3.72g cadmium nitrate (Cd (NO) 3 ) 2 ·4H 2 O) and stirring for 4h, adding 12g thioglycollic acid (TGA) and stirring for 1h to obtain a mixture B; and carrying out hydrothermal reaction on the mixture B for 2 hours at 180 ℃, washing the obtained reaction product by absolute ethyl alcohol, and freeze-drying at-50 ℃ for 12-24 hours to obtain the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with 30% cadmium sulfide loading, wherein the mesoporous carbon nitride/cadmium sulfide composite photocatalyst is marked as mesoporous carbon nitride/cadmium sulfide-30.
Example 4 preparation of a mesoporous carbon nitride/cadmium sulfide catalyst for uranium extraction from seawater, comprising the following steps:
synthesizing mesoporous carbon nitride by a hard template method:
to a 250mL round bottom flask was added 25g cyanamide followed by 12.5 g SiO 2 Nanoparticle dispersion (SiO) 2 The particle size of the nano particles is 12nm, the mass concentration is 40%), 37.5g of mixture A is obtained after uniform mixing, the mixture A is stirred at 80 ℃ for reaction for 8 hours to remove water, the obtained reaction product is placed in a muffle furnace, the temperature is increased at the heating rate of 2 ℃ per minute under the protection of argon, the mixture is calcined at 550 ℃ for 4 hours, and the mixture A is ground and sieved by a 100-mesh sieve after being naturally cooled to room temperature to obtain 32.5g of calcined product; the calcined product was dispersed in 200ml of 3M aqueous ammonia solution of hydrogen fluoride and stirred for reaction for 24 hours to completely remove SiO 2 And washing the template with distilled water and ethanol for 4 times, and finally performing vacuum freeze drying for 12 hours to obtain 20g of mesoporous carbon nitride, wherein the mesoporous carbon nitride is marked as mesoporous carbon nitride-Si-0.2.
Building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst:
2g of mesoporous carbon nitride is ultrasonically dispersed in 200ml of deionized water to obtain mesoporous carbon nitride suspension with 1% of solid content; 4g glucose and 6.2g cadmium nitrate (Cd (NO) 3 ) 2 ·4H 2 O) and stirring for 4h, adding 12g thioglycollic acid (TGA) and stirring for 1h to obtain a mixture B; and carrying out hydrothermal reaction on the mixture B for 2 hours at 190 ℃, washing the obtained reaction product by absolute ethyl alcohol, and freeze-drying at-50 ℃ for 12-24 hours to obtain the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with 50% cadmium sulfide loading, wherein the mesoporous carbon nitride/cadmium sulfide composite photocatalyst is marked as mesoporous carbon nitride/cadmium sulfide-50.
Comparative example 1:
preparing carbon nitride: under the protection of argon, 25g of cyanamide is placed in a muffle furnace, heated to 550 ℃ at a speed of 2 ℃/min, and sintered for 4 hours. The product is ground after being cooled to room temperature and is sieved by a 100-mesh sieve, so as to obtain 20g of carbon nitride yellow powder; the phase composition and specific surface area were tested and photocatalytic performance was tested in an SGY-II type photochemical reaction apparatus.
Comparative example 2:
preparing cadmium sulfide: 6.2g of cadmium nitrate (Cd (NO) 3 ) 2 •4H 2 O) and 4g glucose were dispersed in 200mL deionized water, and after stirring for 4 hours, 12g thioglycolic acid (TGA) was added to the mixture and stirring was continued for 1 hour. The resulting mixture was then transferred to an autoclave, heated at 180 ℃ for 2 hours, centrifuged to collect the product, washed 4 times with water, ethanol, and finally freeze-dried to obtain 2.8g of cadmium sulfide powder, and tested for photocatalytic performance in an SGY-II type photochemical reactor.
The materials obtained in examples 1 to 4 and comparative examples 1 to 2 were subjected to photocatalytic performance test, and the test procedure was as follows: adding 75 mg catalyst powder, 0.375 mLU (VI) standard solution and deionized water into a 25 mL quartz test tube to make the total volume 15 mL, and adjusting the pH value to 6.0; before the photocatalytic reaction, the dark adsorption reaction is carried out for 120min under the dark condition so as to reach the adsorption-desorption balance. Then under the irradiation of xenon lamp and natural light, taking out 1mL of suspension at fixed time intervals, and filtering with a fiber water system filter membrane with the thickness of 0.22 mu m; determination of U (VI) concentration, cd in the filtrate using ICP-OES or UV-Vis spectrophotometer 2+ The concentration of (2) was determined by ICP-OES and each data was tested 3-5 times in parallel and averaged.
The photocatalytic performance test is carried out in an SGY-II photochemical reaction instrument, and the photocatalytic reaction rate is calculated by using a first-order kinetic formula:
wherein,C t andC 0 the concentration of U (VI) in the filtrate at the time t and the initial concentration (M) of U (VI) are respectively;kis the reaction rate constant (min −1 ）。
Characterization of mesoporous carbon nitride/cadmium sulfide composite photocatalyst and evaluation of photocatalytic reduction U (VI) performance thereof
Composition analysis:
fig. 1 (left) shows an XRD spectrum of mesoporous carbon nitride. The mesoporous carbon nitride samples showed characteristic diffraction peaks at 13.1 °, 17.8 ° and 27.4 °, corresponding to the (100), (600) and (002) crystal planes of carbon nitride, respectively. FIG. 1 (right) shows XRD patterns of cadmium sulfide and mesoporous carbon nitride/cadmium sulfide composite photocatalyst, diffraction peaks of cadmium sulfide at 24.5 °, 26.2 °, 27.7 °, 43.4 °, 47.3 ° and 51.5 ° can be respectively assigned to (100), (002), (101), (110), (103) and (112) crystal planes of hexagonal wurtzite.
Diffraction peaks of carbon nitride and cadmium sulfide can be obviously found from the XRD pattern of the mesoporous carbon nitride/cadmium sulfide composite material, and successful preparation of the composite photocatalyst is confirmed.
Specific surface area, pore size distribution and photocurrent analysis:
increasing the specific surface area of carbon nitride and the separation efficiency of photo-generated carriers are key to improving the light absorption capacity of carbon nitride materials and enhancing the photocatalytic reduction U (VI) performance of the carbon nitride materials. Compared with the big holes>50 nm) structure, the pore distance of the mesoporous structure (2-50 nm) is shorter, so that carriers are more easily migrated to the surface, and the transport of reactants or solvents is more facilitated. In addition, the abundant mesopores can enhance the multiple scattering and refraction of light in the catalyst so as to improve the utilization efficiency of the light. From the nitrogen adsorption-desorption isotherms of the prepared samples, it can be seen that the original carbon nitride showed weak N 2 Adsorption, indicating that it is a non-porous structure; the mesoporous carbon nitride samples all show IV-type isotherms, which indicate that the mesoporous carbon nitride samples have mesoporous characteristics; the pore size distribution curve shows that the average pore size of the mesoporous carbon nitride samples is close to 12nm, and the existence of mesopores is further confirmed.
TABLE 1 specific surface area, pore volume, average pore size and photo-current values of carbon nitride and mesoporous carbon nitride
As can be seen from Table 1, it was found that the catalyst was mixed with carbon nitride (specific surface area 8.3 m 2 Per gram, total pore volume 0.04cm 3 Compared with the mesoporous carbon nitride material, the specific surface area and the pore volume of the mesoporous carbon nitride material are obviously improved (35.2-197.6 m) 2 /g，0.14~0.51cm 3 And/g), the high specific surface area and the abundant pore structure are beneficial to improving the light utilization efficiency of the catalyst and the dispersibility in the water system.
Mesoporous carbon nitride exhibits higher photocurrent intensity than carbon nitride, and in particular mesoporous carbon nitride-Si-0.4 has the highest photocurrent (4.46 μa·cm) −2 ) Is carbon nitride (1.20. Mu.A.cm) −2 ) 3.7 times of (3). Therefore, the mesoporous carbon nitride material has greatly increased specific surface area and abundant mesopores, enhances visible light absorption, shortens carrier transmission distance, and promotes carrier separation. It is further confirmed by time resolved PL spectra that the average fluorescence lifetime of mesoporous carbon nitride-Si-0.4 (59 ns) is 1.6 times that of carbon nitride (37 ns), and longer intrinsic fluorescence lifetime is beneficial to increase the transport rate of photogenerated carriers.
In summary, the introduction of mesopores into the carbon nitride material plays a key role in charge separation, increasing visible light absorption, improving photocatalytic activity, and the like, due to the larger surface area, stronger light absorption, and carrier separation efficiency.
And (3) microscopic morphology analysis:
FIG. 2 is a TEM image of cadmium sulfide, mesoporous carbon nitride, and mesoporous carbon nitride/cadmium sulfide composite photocatalyst. From the figure, the cadmium sulfide nano particles are in a regular sphere shape, the size is between 11 and 20nm, and the mesoporous carbon nitride has a typical lamellar structure. After being compounded with cadmium sulfide, a large number of cadmium sulfide nano particles are distributed on the surface of the mesoporous carbon nitride. Further, the HRTEM image shows clear lattice fringes, the lattice spacing is 0.334nm and 0.358nm respectively, and the lattice fringes are consistent with the (002) and (100) planes of cadmium sulfide, so that the successful coupling of carbon nitride and cadmium sulfide to form a heterostructure is proved.
Photocatalytic reduction performance analysis:
as can be seen from the band gap value comparison (table 2) of the carbon nitride, cadmium sulfide and mesoporous carbon nitride/cadmium sulfide materials, the energy band of the mesoporous carbon nitride/cadmium sulfide composite material is significantly reduced to 0.64eV compared to carbon nitride and cadmium sulfide, which is beneficial to capturing more photons for the photocatalytic reaction. The photoluminescence spectrum further proves that the average fluorescence lifetime (37.80 ns) of the mesoporous carbon nitride/cadmium sulfide composite material is 1.37 times and 3.79 times that of carbon nitride (27.54 ns) and cadmium sulfide (9.91 ns), respectively, the intrinsic fluorescence lifetime is longer, and the transmission rate of photo-generated carriers is higher.
TABLE 2 comparison of band gap values of mesoporous carbon nitride/cadmium sulfide materials and photocatalytic reduction rates to U (VI)
The photocatalytic reduction kinetics are shown in FIG. 3, and after 120min adsorption experiments in the dark, the adsorption rate of carbon nitride to U (VI) is lower than 30%, while the adsorption rate of cadmium sulfide to U (VI) is about 34%, and the adsorption of U (VI) on the mesoporous carbon nitride/cadmium sulfide composite material is further enhanced (37%). In the subsequent photocatalytic reduction process, the photocatalytic removal of U (VI) by carbon nitride (lower photocatalytic activity) is negligible in 60min, all U (VI) can be reduced and removed by cadmium sulfide in 60min without a sacrificial agent, and the photocatalytic reduction efficiency of U (VI) by the mesoporous carbon nitride/cadmium sulfide composite material is greatly improved, wherein the mesoporous carbon nitride/cadmium sulfide-30 and the mesoporous carbon nitride/cadmium sulfide-50 have higher photocatalytic reduction efficiency on U (VI), and U (VI) can be completely removed in 20min, namely, the reaction rate of the mesoporous carbon nitride/cadmium sulfide-30 is 9.8 times and 59.63 times that of cadmium sulfide and carbon nitride (methanol is used as an electron donor) (see table 2).
Thus, the introduction of cadmium sulfide can significantly improve the photoactivity of mesoporous carbon nitride, especially without any electron donor involved in the reaction. Therefore, the mesoporous carbon nitride/cadmium sulfide composite material has obviously enhanced photocatalytic reduction activity on U (VI) due to the introduction of mesopores and in-situ construction of the heterostructure composite material, which results in stronger U (VI) adsorption affinity, higher light absorption, narrower band gap, higher carrier separation capability and longer carrier service life.
In consideration of extremely low concentration of U (VI) in natural seawater, the mesoporous carbon nitride/cadmium sulfide composite photocatalyst is further developed to add standard seawater (from Bohai sea, 1.0X10 −6 MU (VI)) and the photocatalytic reduction removal rate change curve of U (VI) are shown in FIG. 4. Under illumination, U (VI) in the marked seawater can be mesoporous within 20minThe carbon nitride/cadmium sulfide composite photocatalyst is rapidly reduced, and excellent U (VI) extraction performance is shown. Meanwhile, the mesoporous carbon nitride/cadmium sulfide composite photocatalyst is proved to recover 80% of marked U (VI) from brine in 3h of illumination, and coexisting cations (such as Ca, co, er, mg, zn, ni and the like) with the concentration equivalent to that of the U (VI) are simultaneously added into a photocatalytic system, so that the composite photocatalyst still shows high selectivity to the U (VI).
Uranium recovery and catalyst recycling performance analysis:
the U (VI) mother solution with the initial concentration of 8.4 and mM is continuously injected into the system, and the extraction capacity of the mesoporous carbon nitride/cadmium sulfide photocatalyst to U (VI) is 2,379 mg/g, which is far higher than that of the traditional physicochemical adsorption method. Deposition of UO on surface 2+x After this time, the color of the sample changed from pale yellow to dark gray. As shown in table 3, after the photocatalytic reaction was completed, the reaction product powder was collected and dispersed in pure water, and after continuously stirring in air for 18.5 hours, 60% of uranium precipitate could be released; further adding 0.1M Na to the mixture 2 CO 3 After the solution is obtained, uranium can be completely eluted and recovered, and the whole elution process is simple, efficient and pollution-free.
TABLE 3 elution Rate Change of uranium deposit
The cyclic catalysis test proves that the mesoporous carbon nitride/cadmium sulfide composite photocatalyst still shows excellent photocatalytic activity after three cycles, and all U (VI) in the system can be removed within 20min in each cycle. Rate constant corresponding to tertiary circulationk) 0.274, 0.228 and 0.227 min, respectively −1 Indicating that the photocatalytic reaction activity does not significantly decrease after three cycles.
Monitoring catalytic Process for the presence/absence of Cd 2+ Releasing:
when pure cadmium sulfide is used as a catalyst, cd detected in the liquid phase increases with the irradiation time 2+ The concentration is gradually increased, which is obviously different from the pure cadmium sulfide system, and the mesoporous carbon nitride/cadmium sulfide composite photocatalystThe catalyst does not release Cd in the process of photocatalytic reduction of U (VI) 2+ (see fig. 5), illustrating that the mesoporous carbon nitride/cadmium sulfide composite material does not undergo decomposition of cadmium sulfide during photocatalytic reduction of U (VI).
Therefore, the composite catalyst can be used for realizing the separation and recovery of uranium in an efficient, green and economic mode, and has important practical significance for extracting uranium from seawater.
Claims (7)
1. The preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater comprises the following steps:
synthesizing mesoporous carbon nitride by a hard template method:
by reacting cyanamide with SiO 2 Uniformly mixing the nanoparticle dispersion liquid to obtain a mixture A, stirring the mixture A at 70-80 ℃ for reaction for 8-12 h, calcining the obtained reaction product for 4h at 550 ℃ in argon atmosphere, cooling and grinding to obtain a calcined product; dispersing the calcined product in 3-4M hydrogen fluoride ammonia water solution, stirring and reacting for 24 hours, washing, and vacuum freeze-drying for 12 hours to obtain mesoporous carbon nitride;
building a mesoporous carbon nitride/cadmium sulfide composite photocatalyst:
ultrasonically dispersing the mesoporous carbon nitride in deionized water to obtain a mesoporous carbon nitride suspension with the solid content of 1-2%; glucose and cadmium nitrate are sequentially added into the mesoporous carbon nitride suspension, stirring is carried out for 4 hours, thioglycollic acid is added, and stirring is continued for 1 hour to obtain a mixture B; carrying out hydrothermal reaction on the mixture B for 2 hours at 170-190 ℃, washing the obtained reaction product by absolute ethyl alcohol, and freeze-drying to obtain the mesoporous carbon nitride/cadmium sulfide composite photocatalyst with 5-50% of cadmium sulfide loading; the mesoporous carbon nitride: glucose: the mass ratio of thioglycollic acid is 1:2:6.
2. the preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater according to claim 1, wherein the preparation method comprises the following steps: the steps include 2 SiO in nanoparticle dispersion 2 The particle size of the nano particles is 11-13 nm, and the mass concentration is 35-45%.
3. The preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater according to claim 1, wherein the preparation method comprises the following steps: in the step (A), the mass concentration of the cyanamide in the mixture A is 8-12%.
4. The preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater according to claim 1, wherein the preparation method comprises the following steps: the steps include 2 The mass ratio is 1.0:0.1 to 1.0:0.8.
5. the preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater according to claim 1, wherein the preparation method comprises the following steps: the calcining heating rate is controlled to be 2-3 ℃/min in the step.
6. The preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater according to claim 1, wherein the preparation method comprises the following steps: the mass volume ratio of the calcination product to the hydrogen fluoride ammonia solution in the step (A) is 1:20.
7. the preparation of the mesoporous carbon nitride/cadmium sulfide catalyst for extracting uranium from seawater according to claim 1, wherein the preparation method comprises the following steps: the freeze drying condition in the step is that the temperature is-50 ℃ and the time is 12-24 hours.
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