CN115193450A - NiS quantum dot modified CdS/WO 3 Heterojunction photocatalyst and preparation method thereof - Google Patents
NiS quantum dot modified CdS/WO 3 Heterojunction photocatalyst and preparation method thereof Download PDFInfo
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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
- B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
- B01J27/04—Sulfides
- B01J27/047—Sulfides with chromium, molybdenum, tungsten or polonium
- B01J27/049—Sulfides with chromium, molybdenum, tungsten or polonium with iron group metals or platinum group metals
-
- B01J35/39—
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
- C01B3/042—Decomposition of water
-
- 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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
NiS quantum dot modified CdS/WO 3 A heterojunction photocatalyst and a preparation method thereof belong to the fields of photochemical energy conversion and photocatalytic degradation. The invention aims to solve the technical problems of low conversion efficiency of photochemical energy and inhibition of light corrosion by surface modification of sulfide in a photocatalytic reaction. The method comprises the following steps: 1. dissolving cadmium nitrate tetrahydrate and thiourea in ethylenediamine, stirring, transferring to a reaction kettle for solvothermal reaction, naturally cooling, washing and drying to obtain the CdS nanorod. 2. Dissolving thiourea and nickel acetate tetrahydrate in water, dispersing the CdS nanorods obtained in the first step in a mixed solution, and then performing hydrothermal treatment to obtain NiS-CdS; 3. dissolving sodium tungstate dihydrate in water, adding hydrochloric acid and oxalic acid in sequence, and carrying out hydrothermal treatment to obtain WO 3 Nanosheets. 4. Preparing the step twoNiS-CdS and WO prepared in step three 3 Dispersing in deionized water, adjusting pH of the solution to make CdS and WO 3 The electrical property of the surfaces is opposite, the two forms interface contact based on electrostatic adsorption, the product is annealed in nitrogen, and finally NiS-CdS/WO is obtained 3 。
Description
Technical Field
The invention belongs to the fields of photochemical energy conversion and photocatalytic degradation.
Background
Photosynthesis is an important means for energy transfer and conversion in the nature, and is also an important inspiration source for the scientific community to develop new technologies and new materials for bionic research. Since the advent of photocatalytic technology, which has received wide attention due to its great potential for development in new energy production and environmental improvement, photocatalytic technology, which is dominated by semiconductor materials, can drive photochemical reactions with sunlight as an energy source under mild conditions, and transfer and convert energy. Inspired by natural photosynthesis, two semiconductor materials meeting the requirements of II-type heterojunction in an energy band structure are selected as a PSI and PS II photoreaction system, and the Fermi level positions of the two materials are higher than that of PS II, so that the full solid direct Z-scheme photocatalyst constructed by the two semiconductors meets the thermodynamic requirements of photocatalytic reaction; a separation path is also spatially manufactured for the photo-generated electron-hole pairs, so that the separation efficiency of photo-generated charges is improved; and meanwhile, coupling narrow-band semiconductor photocatalyst can be selected to realize high-efficiency utilization of solar spectrum. Moreover, the Z reaction can compromise two half reactions of proton reduction and water oxidation to realize the full decomposition of water, once hydrogen and oxygen keep the stoichiometric ratio output, the photolysis water reaction can be continuously carried out. The aim is achieved, and the long-term utilization of the catalyst is realized, so that the hydrogen production technology by photolysis water is expected to advance industrialization. Therefore, research and construction of the novel Z reaction photocatalyst have important practical significance and research value for promoting and realizing efficient photochemical energy conversion, and are leading-edge hotspots in the current photocatalytic research field.
Metal sulfides have a narrower band gap relative to conventional metal oxides because their valence band is composed of the S3 p orbital, with a potential correction relative to the O2 p orbital. CdS is a narrow band gap n-type semiconductor, the band gap is about 2.4 eV, the response capability to visible light is very excellent, the potential of a conduction band is relatively negative, and the reducibility of photo-generated electrons is relatively strong. However, in the actual photocatalytic reaction, oxygen is generated by generating holesTransforming S 2- Produces a photo-corrosion phenomenon and seriously influences the photocatalytic performance of the catalyst. Tungsten oxide (WO) 3 ) Is a typical transition metal oxide, WO 3 Has a small forbidden band width of about 2.7 eV. WO compared to the generally conventional transition metal oxides 3 Has outstanding absorption capability to visible light and is a potential photocatalyst candidate material. But the position of the conduction band is low, resulting in insufficient reduction capability of photo-generated electrons, and the photocatalyst is generally used as an oxidation type photocatalyst.
The two materials have respective advantages and disadvantages, but the energy band structures of the two materials conform to the Z reaction configuration, and the direct Z-scheme photocatalyst is suitable for being constructed. Therefore, aiming at the defects of the materials, the invention provides the non-noble metal promoter NiS quantum dot surface modified CdS/WO 3 A preparation method of a heterojunction photocatalyst. The Fermi energy level of the method by using CdS is higher than that of WO 3 And both exhibit a CdS conduction band bottom higher than that of WO 3 Bottom of guide belt, WO 3 The energy band edge position relation of the valence band top higher than the CdS valence band top can form a Z-type electron transfer mechanism, namely WO under the action of an electric field built in a heterojunction 3 Conduction band electrons will be transferred to the CdS valence band. The space separation of the photo-generated electron-hole pairs generated by the two photocatalysts is realized under a Z-type transfer path, the photo-generated electrons are enriched in a CdS conduction band with high reduction potential, and the photo-generated holes are enriched in WO with high oxidation potential 3 The valence band. Therefore, the method not only achieves higher thermodynamic driving force in photochemical reaction, but also achieves the purpose of protecting CdS from being oxidized by photogenerated holes to inhibit photo corrosion. Meanwhile, the invention adopts non-noble metal NiS quantum dots as a cocatalyst, thereby not only manufacturing more active sites on reaction kinetics, but also abandoning noble metals and reducing material cost.
Disclosure of Invention
The invention provides NiS quantum dot modified CdS/WO aiming at solving the problems that sulfide is easily corroded by light and the catalysis efficiency is low in the photocatalysis reaction 3 A heterojunction photocatalyst and a preparation method thereof; in order to solve the problems, the invention discloses NiS quantum dot modified CdS/WO 3 Heterojunction photocatalysisThe preparation and the preparation method thereof are completed by the following steps.
Dissolving cadmium nitrate tetrahydrate and thiourea in ethylenediamine and stirring. And then transferring the solution into a reaction kettle with a polytetrafluoroethylene lining for heating, cooling, washing, and drying in a vacuum drying oven to obtain CdS.
Dissolving thiourea and nickel acetate tetrahydrate in water, dispersing the CdS nano rod obtained in the step one in a mixed solution, performing ultrasonic oscillation, performing hydrothermal treatment, washing a product, and performing vacuum drying to obtain NiS-CdS;
and step three, dissolving sodium tungstate dihydrate in deionized water, adding hydrochloric acid, stirring for 3 hours, adding oxalic acid, and continuing stirring for 30 minutes. Then transferring the solution into a reaction kettle with a polytetrafluoroethylene lining, carrying out hydrothermal treatment, washing and drying a product to obtain WO 3 Nanosheets.
Step four, the NiS-CdS prepared in the step two and the WO prepared in the step three are mixed 3 Dispersing in deionized water, stirring vigorously, and ultrasonic vibrating. The pH of the solution was then adjusted and stirred vigorously. Drying the product and then annealing in nitrogen to obtain NiS-CdS/WO 3 。
Further limiting, in the first step, 0.96 to 2.88 g of cadmium nitrate tetrahydrate and 0.71 to 2.13 g of thiourea are added into 50 mL of ethylenediamine, and the stirring time in the first step is 30 min.
Further limiting, in the first step, the temperature is kept in an oven at 120 to 180 ℃ for 16 to 24 hours, and in the first step, the temperature is kept in a vacuum drying oven at 60 ℃ for 12 hours.
And further limiting, dissolving 0.63-1.89 mg of thiourea and 2.07-6.22 mg of nickel acetate tetrahydrate in deionized water, adding 212.6-2.126 g of CdS nanorods, and performing ultrasonic oscillation for 30 min in the second step.
Further limiting, in the second step, carrying out hydrothermal treatment at 50-80 ℃ for 2-5 h, and in the second step, carrying out vacuum drying at 60 ℃ for 12 h.
And further limiting, dissolving 1.815 to 4.444 g of sodium tungstate dihydrate in 50 mL of distilled water, adding 8 to 12 mL of hydrochloric acid, and adding 0.45 to 1.35 g of oxalic acid.
And (3) performing hydrothermal treatment at 50-80 ℃ for 16-24 h, and drying at 60 ℃ for 12 h.
Further limiting, the vigorous stirring time in the fourth step is 30 min, and the ultrasonic oscillation time in the fourth step is 10 min.
Further limiting, step four uses 0.01 mol/L HCl solution to adjust the pH of the solution to 3.
Further defined, step four was dried at 60 ℃ for 12 h, and step four annealed the sample at 380 ℃ under nitrogen for 2 h.
NiS quantum dot modified CdS/WO prepared by using method 3 The heterojunction photocatalyst has a Z-scheme photo-generated electron transfer path, and can effectively improve the photocatalytic performance of the material and inhibit the sulfide photo-corrosion phenomenon; in addition, the non-noble metal cocatalyst can be used for effectively controlling the material cost; the invention provides a new scheme for preparing a heterojunction, namely a composite material synthesis strategy combining chemical in-situ growth and physical electrostatic adsorption.
Drawings
FIG. 1 is NiS-CdS/WO 3 A synthetic route of the composite material; FIG. 2 is CdS, WO 3 NC7 and different components NiS-CdS/WO 3 An XRD pattern of the composite material; FIG. 3 is a TEM photograph of CdS nanorods; FIG. 4 is WO 3 A nano-sheet TEM photograph; FIG. 5 is a HRTEM photograph of an NC7 sample; FIG. 6 is an HRTEM photograph of NCW 10; FIG. 7 is a graph showing the degradation concentration of each sample against a 40 mg/L potassium dichromate solution with time; FIG. 8 is a graph showing the degradation rate of each sample in a 40 mg/L potassium dichromate solution; FIG. 9 is a cycle stability test of NCW10 samples; FIG. 10 is a graph showing the change in hydrogen content over time in each sample from photolysis; fig. 11 is a comparison of the photolytic hydrogen production rate of each sample.
Detailed Description
Example 1: the CdS nanorod used in this example was prepared as follows: dissolving 1.92 g of cadmium nitrate tetrahydrate and 1.42 g of thiourea in 50 mL of ethylenediamine, vigorously stirring at 300 rpm for 30 min, transferring to a reaction kettle with a polytetrafluoroethylene lining of 100 mL, heating in an oven at 160 ℃ for 24 h, cooling to room temperature, repeatedly washing with deionized water and absolute ethyl alcohol, finally vacuum-drying at 60 ℃ for 12 h, and taking out for later use.
In the implementation, niS quantum dot modified CdS/WO 3 The heterojunction photocatalyst and the preparation method thereof are completed by the following steps:
step one, adopting a hydrothermal method, dissolving 1.26 mg of thiourea and 4.14 mg of nickel acetate tetrahydrate in 45 mL of deionized water. The prepared CdS nanorods (212.6 mg, 637.8 mg, 1.488 g, 2.126 g) were then added to the above solutions, respectively, and the mixture was sonicated for 30 min, then hydrothermally treated at 60 ℃ for 3 h, and washed with water and ethanol. Finally the solid was dried under vacuum at 60 ℃. Wherein the mol percentages of the NiS nanorod and the CdS nanorod are respectively 1at%,3at%,7at% and 10at%, and are respectively marked as NC1, NC3, NC7 and NC10.
Step two, synthesizing WO by using a hydrothermal method 3 First, 3.629 g of sodium tungstate dihydrate was dissolved in 50 mL of deionized water, 10 mL of hydrochloric acid was added, and the mixture was stirred at 300 rpm at room temperature for 3 hours. Then 0.900 g oxalic acid was added to the above solution and stirring was continued for 30 min. And finally transferring the reaction solution to a reaction kettle with a polytetrafluoroethylene lining for hydrothermal treatment at 60 ℃ for 24 hours. And repeatedly washing the product with deionized water and absolute ethyl alcohol, drying the product in vacuum at the temperature of 60 ℃ for 12 hours, and taking the product out for later use.
Step three, synthesizing NiS-CdS/WO with different component ratios by adopting an electrostatic adsorption method 3 The composite material determines the optimal loading amount of NiS to be 7at% according to the photocatalytic activity of NiS-CdS series materials, thereby being matched with WO 3 And selecting the NiS-CdS for compounding as NC7. The pH of the dispersion was adjusted to 3 by 0.01 mol/L hydrochloric acid solution, NC7 and WO 3 The mixture is dispersed in 50 mL deionized water according to the proportion, and is subjected to ultrasonic treatment for 10 minutes and vigorous stirring for 60 minutes. NC7 and WO 3 The mass ratio of (A) to (B) is 100:5,100: 10, 100:15 and 100:20, designated NCW5, NCW10, NCW15 and NCW20, respectively. The samples were collected by centrifugation and dried at 60 ℃ for 12 h, and finally annealed at 380 ℃ under nitrogen for 2 h.
The light-catalyzed degradation adopts a 300W xenon lamp as a light source. 20 mg of sample powder to be tested and 30 mL of 40 mg/L potassium dichromate solution are placed in a 100 mL beaker. And (3) placing the beaker on a stirring table in front of a light source, fixing the distance between the beaker and the light source to be 5 cm, and keeping constant-speed magnetic stirring in the degradation reaction process. And (3) carrying out absorbance detection on the reaction solution at the same time interval, calculating the concentration of the reaction solution, and making a curve of the degradation rate and the illumination time, thereby analyzing and comparing the photocatalytic activity of the sample.
As can be seen from FIG. 7, the NCW10 sample has the fastest degradation rate in the photocatalytic reaction, all potassium dichromate is degraded in 6 minutes, and the degradation rate reaches 33.3. Mu. Mol.h -1 ·g cat -1 . It can be seen that the cycle stability of the NCW10 sample is good, and after five photocatalytic degradations, the catalytic performance still remains 93.7%. The improvement of degradation rate and cycle stability shows that the Z-type heterojunction plays an important role in space charge separation, and the supported NiS quantum dot cocatalyst not only increases the number of surface reaction active sites, but also effectively protects the photo-reduction catalyst CdS from photo-corrosion.
The specific method for testing the photocatalytic hydrogen evolution comprises the steps of weighing 20 mg of solid powder catalyst in a sealed system and dispersing in 60 mL of deionized water and 20 mL of lactic acid. The test system consisted essentially of a quartz tube and a sealed system, and prior to photocatalytic testing, the apparatus was purged with Ar gas flow to remove air, and then the reaction system was evacuated for 30 minutes to remove dissolved gases and ensure vacuum conditions. Photocatalytic water splitting experiments were performed at room temperature and the product was determined with a gas chromatograph (GC 7920, thermal Conductivity Detector (TCD), argon carrier gas) using a 300W xenon lamp with a cut-off filter (λ >420 nm) as the light source.
The change rule of the photolysis water hydrogen of the sample along with the time is also shown in the figure 10, and it can be seen that the hydrogen production rate of the NCW10 sample is obviously superior to that of the same series of materials, and the rate is 70.73 mmol.h -1 ·g cat -1 The CdS quantum dot catalyst is 7 times of reference CdS and nearly 2 times of reference NC7, and shows that the photocatalytic hydrogen production performance of the material is greatly improved under the synergistic effect of a Z-scheme photon-generated carrier transfer path and a non-noble metal NiS quantum dot catalyst promoter.
Claims (10)
1. NiS quantum dot modified CdS/WO 3 Heterojunction photocatalyst, preparation method thereof and application thereofCharacterized in that the preparation method is completed by the following steps: dissolving cadmium nitrate tetrahydrate and thiourea in ethylenediamine, stirring, transferring the solution to a reaction kettle with a polytetrafluoroethylene lining, heating, cooling, washing, and drying in a vacuum drying oven to obtain CdS; dissolving thiourea and nickel acetate tetrahydrate in water, dispersing the CdS nanorods obtained in the step one in a mixed solution, performing ultrasonic oscillation, performing hydrothermal treatment, washing products, and performing vacuum drying to obtain NiS-CdS; step three, dissolving sodium tungstate dihydrate in deionized water, adding hydrochloric acid, stirring for 3 hours, adding oxalic acid, continuing stirring for 30 minutes, transferring the solution to a reaction kettle with a polytetrafluoroethylene lining, carrying out hydrothermal treatment, washing a product, and drying to obtain WO 3 (ii) a Step four, the NiS-CdS prepared in the step two and the WO prepared in the step three are mixed 3 Dispersing in deionized water, ultrasonically oscillating, adjusting pH value of the solution, violently stirring at 300 rpm, drying the product, and annealing in nitrogen to obtain NiS-CdS/WO 3 。
2. The method according to claim 1, wherein 0.96 to 2.88 g of cadmium nitrate tetrahydrate and 0.71 to 2.13 g of thiourea are added to 50 mL of ethylenediamine in the first step, and the stirring time is 30 min.
3. The method according to claim 1, wherein in the first step, the temperature is kept in an oven at 120 to 180 ℃ for 16 to 24 hours, and the temperature is kept in a vacuum drying oven at 60 ℃ for 12 hours.
4. The method according to claim 1, characterized in that, in the second step, 0.63 to 1.89 mg of thiourea and 2.07 to 6.22 mg of nickel acetate tetrahydrate are dissolved in deionized water, 212.6 to 2.126 g of CdS nanorods are added, and the mixture is subjected to ultrasonic oscillation for 30 min.
5. The method according to claim 1, wherein in the second step, the mixture is subjected to hydrothermal treatment at 50 to 80 ℃ for 2 to 5 hours, and then dried under vacuum at 60 ℃ for 12 hours.
6. The method of claim 1, wherein 1.815 to 4.444 g of sodium tungstate dihydrate are dissolved in 50 mL of distilled water in the third step, and then 8 to 12 mL of hydrochloric acid and 0.45 to 1.35 g of oxalic acid are added.
7. The method according to claim 1, wherein the third step is carried out by hydrothermal treatment at 50 to 80 ℃ for 16 to 24 hours, and drying at 60 ℃ for 12 hours.
8. The method according to claim 1, wherein the vigorous stirring time in the fourth step is 30 min, and the ultrasonic oscillation time is 10 min.
9. The method of claim 1, wherein the pH of the solution is adjusted to 3 in step four using 0.01 mol/L HCl solution.
10. The method of claim 1, wherein step four is performed by drying at 60 ℃ for 12 hours and annealing the sample at 380 ℃ under nitrogen for 2 hours.
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| US10456776B1 (en) * | 2019-02-21 | 2019-10-29 | King Saud University | Method of fabricating a photocatalyst for water splitting |
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