CN113856709B - Preparation method of catalyst for photocatalytic decomposition of pure water - Google Patents

Preparation method of catalyst for photocatalytic decomposition of pure water Download PDF

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CN113856709B
CN113856709B CN202111139723.6A CN202111139723A CN113856709B CN 113856709 B CN113856709 B CN 113856709B CN 202111139723 A CN202111139723 A CN 202111139723A CN 113856709 B CN113856709 B CN 113856709B
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deta
pure water
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刘洋
游遨
肖吉
宋金刚
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Guangdong Industry Technical College
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/14Phosphorus; Compounds thereof
    • B01J27/16Phosphorus; Compounds thereof containing oxygen, i.e. acids, anhydrides and their derivates with N, S, B or halogens without carriers or on carriers based on C, Si, Al or Zr; also salts of Si, Al and Zr
    • B01J27/18Phosphorus; Compounds thereof containing oxygen, i.e. acids, anhydrides and their derivates with N, S, B or halogens without carriers or on carriers based on C, Si, Al or Zr; also salts of Si, Al and Zr with metals other than Al or Zr
    • B01J27/1802Salts or mixtures of anhydrides with compounds of other metals than V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, e.g. phosphates, thiophosphates
    • B01J27/1808Salts or mixtures of anhydrides with compounds of other metals than V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, e.g. phosphates, thiophosphates with zinc, cadmium or mercury
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00Catalysts, in general, characterised by their form or physical properties
    • B01J35/30Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/39Photocatalytic properties
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    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/04Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
    • C01B3/042Decomposition of water
    • YGENERAL 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
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    • Y02E60/30Hydrogen technology
    • Y02E60/36Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

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Abstract

The application successfully prepares Zn in a mixed solvent by using a solvothermal method 0.3 Cd 0.7 S/ZnS(DETA) 0.5 And (3) carrying out modification such as phosphorus oxide loading and metal doping on the heterojunction material by utilizing a photochemical synthesis method. Parameters such as crystal structure, forbidden band width, morphology and composition of the prepared sample are characterized in detail by using various means such as XRD, UV-vis DRS, SEM and EDS. The prepared sample was subjected to photocatalytic decomposition pure water test, and found that: (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Pi sample shows the highest hydrogen production rate of pure water by photocatalytic decomposition, and the hydrogen production rate reaches 1.465 mmol.h under the irradiation condition of visible light (lambda is more than 420nm and less than 780 nm) ‑1 ·g ‑1

Description

Preparation method of catalyst for photocatalytic decomposition of pure water
Technical Field
The invention relates to a method for producing hydrogen by photocatalytic water, in particular to a catalyst for decomposing pure water by photocatalysis and a preparation method thereof.
Background
The hydrogen energy is used as a secondary energy, has the advantages of high combustion heat value (the energy density is 143 kJ/g), large reserve (water can be used as a hydrogen source), reproducibility (a combustion product is water, and the water can be reduced into the hydrogen again), convenience in storage and transportation and the like, and can be used for relieving the problems of the existing energy crisis and environmental pollution. Compared with the existing hydrogen production method by fossil fuel, the photocatalytic water splitting hydrogen production method with simple operation and low cost has great technical potential, but the preparation of the photocatalyst with high activity and high stability is still a long-term and difficult challenge. Among the photocatalytic materials, zn x Cd 1-x The S-based catalyst is considered to be one of the most potential photocatalytic materials due to the advantages of controllable energy band structure, high efficiency of photocatalytic partial water decomposition (PPWS) hydrogen production and the like. However, in the application of photocatalytic pure water decomposition, due to the defects of poor stability and low hydrogen production efficiency caused by lack of sacrificial reagent for capturing photoproduction cavities, zn is restricted x Cd 1-x Research and development of S-based catalysts.
The process of photocatalytic decomposition of pure water can be divided into: photocatalytic total decomposition of water (2H) 2 O→2H 2 +O 2 POWS) and photocatalytic intermediate stage decomposition of water (2H) 2 O→H 2 +H 2 O 2 PIWS). Reaction with photocatalytic partial decomposition of water (PPW)S), the photogenerated hole reaction pathways are numerous due to the lack of capture by sacrificial reagents. Except that four electrons (O) are generated 2 ) Transfer of the product and possible formation of a single electron · OH), two electrons (H) 2 O 2 ) Transfer of by-products, wherein H 2 O 2 Will oxidize S 2- Causing catalyst poisoning (CdS + 4H) 2 O 2 →Cd 2+ +SO 4 2- +4H 2 O). Furthermore, zn x Cd 1-x The S-based catalyst can generate the photo-corrosion phenomenon (oxygen-free photo-corrosion: cdS +2 h) + →Cd 2+ + S; aerobic photo etching: cdS +4h + +2H 2 O+O 2 →Cd 2+ +SO 4 2- +4H + ) This allows the water oxidation process to act as a kinetic-determining step for the reaction of decomposing pure water, directly affecting the stability of the catalyst and the efficiency of decomposing pure water.
Given that stability is an important indicator of catalyst application, zn is improved x Cd 1-x The problem of photo-corrosion of S-based catalysts is imperative. Through a large amount of literature research, the following findings are obtained: since the phosphide has metalloid and high stability, zn is transformed into Zn x Cd 1-x After the phosphide cocatalyst is introduced into the S-based catalyst, the problem of photo-corrosion can be effectively relieved. In 2018, the group of problems of the Lugong boiler uses combustible and explosive white phosphorus as a phosphorus source and adopts a hydrothermal method to produce Zn x Cd 1-x Outer layer of S-based catalyst to prepare Ni 2 The P shell material realizes the process of photocatalytic total water decomposition (POWS), and makes AG/Ni dissolved in an artificial cheek (AG) high-efficiency separation system 2 The P/CdS catalytic system shows higher hydrogen production rate (0.838 mmol.h) for decomposing pure water -1 ·g -1 ). In 2020, chenyubin task group utilized high temperature pyrolysis NaH 2 PO 2 The generated virulent PH3 is used as a phosphorus source to prepare RP @ CoP/Cd 0.9 Zn 0.1 An S-type Z-scheme system capable of decomposing pure water in a photocatalytic intermediate-stage water decomposition (PIWS) route, achieving an apparent quantum efficiency of 6.4% at 420 nm. By contrast, it is easy to find that: although the catalyst system is loaded with the phosphide promoter, the photocatalytic decomposition of pure water to produce hydrogen is similar to that of the traditional photocatalytic partThe performance of decomposing water to produce hydrogen is still far from each other. And the modification process with high toxicity and high energy consumption also limits the application space of phosphide. From the perspective of green, safety and energy saving, the rapid and convenient photochemical synthesis method for preparing phosphide has great advantages.
It is known that the preparation of phosphides involves the incorporation of large amounts of phosphate compounds, the effect of which is often overlooked. Recently, the group of zheng distachy topics assembled a NiCoPi modified CdS catalytic system, which found: niCoPi can capture photogenerated electrons and holes of CdS catalyst, thereby generating Ni I CoP and NiCo III Pi, and taking the catalytic site as a catalytic site to carry out photocatalytic hydrogen production and oxidation sacrificial reagent reaction. The phosphate promoter can be used as a hydrogen production promoter and a water oxidation promoter at the same time, and the dual-functional characteristic enables the phosphate promoter to have extremely high application value in the field of photocatalytic pure water. Although the transition metal phosphate catalyst has been widely applied to the field of electrocatalysis and photoelectrocatalysis decomposition of pure water, the transition metal phosphate catalyst is used as a cocatalyst to modify Zn x Cd 1-x The research on the process of photocatalytic decomposition of pure water by using an S-based catalyst is rarely reported.
Disclosure of Invention
In view of the above circumstances, the present inventors have made intensive studies and have found a catalyst for photocatalytic decomposition of pure water and a process for producing the same.
The invention aims to provide a preparation method of a catalyst for photocatalytic decomposition of pure water, which comprises the following steps:
(1)Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 the heterojunction material is dispersed in H 2 PO 2 - In the solution, carrying out ultrasonic treatment under the protection of inert gas;
(2) Then transferring the suspension obtained in the step (1) into a photocatalytic reactor, sealing the container, vacuumizing the whole reaction system by using a vacuum pump, irradiating the reactor by using a visible light source, and keeping the temperature at room temperature and stirring continuously;
(3) After the reaction is finished, opening the reactor, removing supernatant, centrifugally recovering precipitate, drying in an ovenRecovering to obtain phosphate radical modified Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Marked as Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x
(4) Taking Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Sample, dispersed in H containing one or more transition metal salts 2 PO 2 - Ultrasonic treating in water solution under the protection of inert gas, transferring to a photocatalytic reactor, sealing the container, vacuumizing the whole reaction system by using a vacuum pump, irradiating the reactor by using a visible light source, keeping the temperature at room temperature, continuously stirring, opening the reactor after the reaction is finished, removing supernatant, centrifugally recovering precipitate, drying in an oven, and recovering to obtain Zn doped with transition metal 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Namely the catalyst for decomposing pure water by photocatalysis;
the one or more transition metal salts are selected from nickel salts, cobalt salts, iron salts, mixed salts of nickel and iron, and mixed salts of nickel and manganese.
Preferably, the inert other is nitrogen, argon or helium;
preferably, said H 2 PO 2 - The solution is NaH 2 PO 2 、KH 2 PO 2 One of (1);
preferably, the ultrasonic treatment time is 20-60min;
preferably, the vacuum treatment time is 10-30min;
preferably, the visible light source is one of sunlight, a xenon lamp, a mercury lamp, an incandescent lamp, a light-emitting diode lamp and the like, and the treatment time is 2-5h;
preferably, the drying temperature of the oven is 50-70 ℃, and the drying time is 10-15h.
The invention also provides the catalyst for photocatalytic decomposition of pure water, which is prepared by the method.
Compared with the prior art, the invention has the beneficial effects that:
herein, Z is successfully prepared in a mixed solvent by a solvothermal methodn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 And (3) carrying out modification such as phosphorus oxide loading and metal doping on the heterojunction material by utilizing a photochemical synthesis method. Parameters such as crystal structure, forbidden band width, morphology and composition of the prepared sample are characterized in detail by using various means such as XRD, UV-vis DRS, SEM and EDS. The prepared sample was subjected to photocatalytic decomposition pure water test, and found that: (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f The Pi sample shows the highest hydrogen production rate of pure water by photocatalytic decomposition, and the hydrogen production rate reaches 1.465 mmol.h under the irradiation condition of visible light (lambda is more than 420nm and less than 780 nm) -1 ·g -1 . The photochemical synthesis modification strategy with simple operation and low cost opens a new door for the application of the material with easy light corrosion in the field of photocatalytic decomposition of pure water.
Drawings
FIG. 1: zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 SEM image of sample
FIG. 2: zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 X-ray diffraction (XRD) pattern of
FIG. 3: zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Ultraviolet-visible diffuse reflectance spectrum (A), energy band conversion spectrum (B)
FIG. 4: XRD patterns of the respective photocatalysts
FIG. 5: ultraviolet-diffuse reflectance spectrum (A) of each catalyst, band conversion spectrum (B) of each catalyst
FIG. 6: (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f SEM image of Pi sample
FIG. 7: hydrogen production curve diagram of catalyst after metal modification
Detailed Description
Example 1.Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Preparation of the Material
315ml of Diethylenetriamine (DETA) and 35ml of pure water are weighed, mixed and poured into a 500ml big beaker, and 1100mg (5 mmol) of zinc acetate and 1322.5mg (5 mmol) of cadmium acetate are weighed) 2450mg (20 mmol) of L-cysteine is poured into a beaker filled with the mixed solution, each medicine in the beaker is dissolved by a magnetic stirrer and an ultrasonic cleaner, after each medicine is dissolved, the dissolved solution is poured into a reaction kettle, the reaction kettle is screwed and then put into an electric heating constant temperature blast drying oven to react for 24 hours at 180 ℃, and after the reaction stops, the prepared Zn is centrifuged by a centrifuge 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Recovering and putting into an oven for dehydration to obtain yellow powder Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 A material.
Example 2 Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Phosphorus oxide coating of material surface layer
Weighing 180mg of Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 2385mg sodium hypophosphite and into 50ml centrifuge tube, adding 30ml deionized water, under the protection of argon gas, performing ultrasonic treatment in ultrasonic instrument for 30min, pouring the ultrasonic solution into the photosynthetic reactor and adding 50ml deionized water, starting the stirrer, pumping the reactor into a vacuum state by vacuum pump, starting xenon lamp for illumination for 3 hr, and in the illumination process, using NaH 2 PO 2 Capturing photoproduction cavity, assisting catalyst to carry out photocatalytic hydrogen production reaction, and simultaneously utilizing NaH 2 PO 2 Can capture photoproduction electrons, and the phosphorus oxide generated by oxidation and reduction reaction is coated on Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The surface of the material. Completion of Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x And (4) preparing the material.
EXAMPLE 3 photochemical Synthesis experiments
1. Photochemical synthesis experiment of nickel and iron-based cocatalyst: 82mg of prepared Zn is weighed 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Pouring the materials, 38mg of nickel sulfate hexahydrate, 18.5mg of ferric nitrate nonahydrate and 141mg of sodium hypophosphite into a 50ml centrifuge tube together, adding 30ml of deionized water into the centrifuge tube, carrying out ultrasonic treatment for half an hour under the protection of argon, and after the ultrasonic treatment is finished, separating the ultrasonic solution and 50ml of deionized waterPouring the sub-water into a photosynthetic reactor, vacuumizing the reactor by using a centrifugal pump, starting a magnetic stirrer and a xenon lamp light source, illuminating for two hours, closing the xenon lamp and the stirrer after the illumination for two hours, standing the solution in the reactor for more than half an hour, and centrifugally recycling after the material is completely deposited, wherein the material mark is as follows: (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Pi。
2. Photochemical synthesis experiment of nickel and manganese-based cocatalyst: 82mg of prepared Zn are weighed 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Material, 35.7mg nickel sulfate hexahydrate, 9.2mg manganese sulfate monohydrate, and 141mg sodium hypophosphite were added, and the operations in 1 were repeated, and the final resulting material was labeled as: (Zn) a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f Pi。
3. Photochemical synthesis experiment of nickel, manganese, iron and cobalt base single metal cocatalyst: in the process of single metal base cocatalyst photosynthesis, 82mg of prepared Zn is required to be added in each photosynthesis reaction 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Weighing different metal salts (50 mg of nickel sulfate hexahydrate or 33mg of manganese sulfate monohydrate or 77mg of iron nitrate nonahydrate or 56mg of cobalt nitrate hexahydrate) respectively for 141mg of sodium hypophosphite, repeating the operation in the step 1, and marking the finally obtained materials as follows: zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Ni a Pi、(Zn a Cd b Mn c )S/(Zn d Mn e )S/PO x 、(Zn a Cd b Fe c )S/(Zn d Fe e )S/PO x 、Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Co a Pi。
Example 4 Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Is characterized by
To explore Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 And (3) analyzing the morphology of the material by using an SEM scanning electron microscope. As can be seen from FIG. 1A, zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The material is in a micron spherical shape, the size is within the range of 2-4 microns, and after a single micron spherical material is further observed in an enlarged way (figure 1B), a large number of nano particles with different sizes are loaded on the surface layer of the spherical material, and the size is between 50-100 nm. To determine the composition of the catalyst material, we characterized it by EDS, as shown in FIG. 2 and Table 1, the atomic percent Zn/Cd inside the microspheres is about 3: 7, indicating that the true composition of the microsphere material should be Zn 0.3 Cd 0.7 S, which is in clear discrepancy with our Zn/Cd = 1: 1 charge ratio. Due to Zn in the solvothermal process 2+ And Cd 2+ The difference of the complexing ability with diethylenetriamine and L-cysteine, and the larger difference of the solubility product between ZnS and CdS will cause a part of Zn 2+ Can not be fused into Zn x Cd 1-x S solid solution material. In the EDS analysis, a large amount of C and N elements can be found, which obviously comes from diethylenetriamine molecules complexed on the surface of the material, and the loss of Zn in the feeding materials is proved 2+ For generating ZnS (DETA) 0.5 Material and exhibits a ribbon-like morphology. We observed that the microsphere surface layer was wrapped with some strip-like material, indicating that Zn was successfully prepared 0.3 Cd 0.7 S/ZnS(DETA) 0.5 A heterojunction material.
TABLE 1 Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Electronic dispersion energy spectrum meter
Figure BSA0000253708240000041
FIG. 2 shows Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The XRD pattern of the material is found by comparison: zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The XRD diffraction peak of the material is positioned between cubic phase ZnS (PDF # 05-0566) and hexagonal phase CdS (PDF # 41-1049) card peaks, and the Zn prepared by the subject group is illustrated 0.3 Cd 0.7 The S material is solid solution material instead of mixture of ZnS and CdS, and Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The material exhibits typical hexagonal phase diffraction peaks.
As can be observed from the ultraviolet diffuse reflectance chart 3A, the absorption edge band of the raw material is about 500 nm. FIG. 3B is a band conversion diagram of the material, and it can be understood from the conversion that the band gap width of the raw material is 2.52eV, and these parameters indicate Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The material is an excellent visible light response photocatalyst.
Example 5 characterization of modified catalyst Material
As shown in FIG. 4, with Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 In contrast, zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x 、(Zn a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Pi、(Zn a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f Pi、Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Ni a Pi、(Zn a Cd b Mn c )S/(Zn d Mn e )S/PO x 、(Zn a Cd b Fe c )S/(Zn d Fe e )S/PO x And Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Co a No significant change in the peak position of samples such as Pi and the like occurred, and no new diffraction peak was generated. The phosphorus oxide protective layer and the phosphate cocatalyst which are deposited on the surface layer are amorphous structures after two-step photochemical synthesis, and the amorphous metal phosphate (Ni) a Pi or Co a Pi) material, the internal transition metal can realize the self-healing characteristic of the material through valence change, and hopefully help the material to convert between phosphate and phosphide, so that the material has great application potential in the process of decomposing pure water by photocatalysis.
As shown in FIG. 5A, we tested Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 、Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x 、(Zn a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Pi and (Zn) a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f Uv-diffuse reflectance spectrum of Pi. With Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 In contrast, zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x And (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f The Pi sample has no obvious change in absorption intensity and no obvious shift of the absorption band edge, and the absorption band edge is in the range of 500-510 nm. In contrast to the three samples described above, (Zn) a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f Pi showed high photoresponse in the spectral range of 300-800 nm, with the absorption edge shifted to around 550 nm.
We further converted the band gaps of the four samples by the Kubelka-Munk formula. As shown in FIG. 5B and Table 2, zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 、Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x 、(Zn a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f The band gap values of the three Pi samples are not very different and are respectively 2.52eV, 2.54 eV and 2.53eV, which shows that the three Pi samples have excellent visible light response capability. (Zn) a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f The Pi sample exhibits the smallest bandgap value (2.43 eV). These results illustrate that: after a single photochemical synthesis process, the deposited protective layer of phosphorus oxide may modify ZnS (DETA) inside the raw material 0.5 The sulfur vacancy defect state of the components causes the band gap of the material to be slightly widened, but the overall transformation is not large; in the second step of photochemical synthesis, zn may be present in Fe, mn and other ions due to cation exchange 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Doping of the material to form (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Pi and (Zn) a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f The band gap of the Pi samples, produced a different degree of degradation. The narrower energy band gap means higher photoresponse capability and higher photon capture efficiency, so that higher density of photon-generated carriers are generated, and the efficiency of hydrogen production by photolysis of a catalytic system is improved.
TABLE 2 band gap Width (E) g ) Watch (A)
Figure BSA0000253708240000051
Figure BSA0000253708240000061
We are right (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Pi samples were characterized by SEM (fig. 6). As shown in the figure, after two-step photochemical synthesis modification, (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f The Pi sample still exhibited a microspherical morphology with a particle size between 1.4 and 5 μm, with the microspherical surface surrounding the ribbon of material, which should be ZnS (DETA) 0.5 The components being converted to (Zn) in a two-step photochemical synthesis d Fe e ) And (4) an S material. After further amplification, it was found that: the micron spherical material is actually in a ball-rod shape assembled by countless nano rods, and is observed in Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The nanoparticles on the surface layer of the material may be similar to nanoparticles because the nanorods are densely packed and we only see the tips of the nanorods. To verify the composition of these materials, we performed EDS analysis on them and found that: the surface layer of the material has Ni, P, O and other element distribution, but has no Fe element distribution, which indicates that Fe element is doped into the interior of the sulfide raw material, and transition metal phosphate loaded on the surface layer is changed into Ni d Pi。
TABLE 3 (Zn) a Cd b Fe c )/S/PO x /(Fe d Ni e ) Pi electronic dispersion energy spectrum meter
Figure BSA0000253708240000062
Example 6 photocatalytic intermediate stage decomposition pure Water Performance test of modified catalyst Material
The prepared sample is subjected to a photocatalytic decomposition pure water hydrogen production test, and the specific steps are entered:
30mg of a sample to be tested is weighed, dispersed in 80ml of ultrapure water and subjected to ultrasonic treatment for 30min under the protection of argon. Then the suspension was transferred to a photocatalytic reactor, and after the vessel was sealed, the entire reaction system was vacuumed with a vacuum pump for 15min. Irradiating the reactor with visible light source (300W xenon lamp equipped with 420nm front cut-off filter), maintaining room temperature, stirring, passing gas generated by the system through chromatography (Tianmei GC7900, TCD, ar as carrier gas,
Figure BSA0000253708240000072
molecular sieve column), and performing quantitative analysis.
The results are shown in FIG. 7. Under the irradiation condition of visible light (420 nm & lt lambda & lt 780 nm), zn exists due to serious photo-corrosion phenomenon 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The material does not exhibit hydrogen production performance in pure water, so we do not show the performance parameters of this sample in the figures, tables. In contrast, zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x And (Zn) a Cd b Mn c )S/(Zn d Mn e )S/PO x The sample shows the capacity of producing hydrogen by decomposing pure water through photocatalysis, a hydrogen peak is found in gas chromatography, but the hydrogen production area is too small, and the system cannot calculate the peak area, so that the map of the sample is not shown in figure 7. The reason why the hydrogen-producing performance is from inexistence to existence is presumed to be that Zn is subjected to the first step of photochemical synthesis 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The surface layer of the material is covered with a layer of phosphorus oxide, and the amorphous substance can be used as a protective layer to effectively delay Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The material has a photo-corrosion effect caused by contact with dissolved oxygen in water, and the hydrogen production performance of the material cannot be effectively improved by singly doping Mn element. The photocatalytic hydrogen production performance of the rest samples is as follows: (Zn) a Cd b Fe e )S/(Zn d Fe e )S/PO x 、Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Co a Pi、Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Ni a Pi、(Zn a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f Pi、(Zn a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f The sequence of Pi was sequentially enhanced, and the hydrogen production rate thereof was as shown in table 4.
According to recent research, niCoPi material can synchronously capture photogenerated electrons and holes in the process of photocatalytic hydrogen production so as to convert the photogenerated electrons into Ni I CoP and NiCo III Pi is used. Then Ni I CoP and NiCo III Pi is further used to collect photo-generated electrons and holes for photocatalytic reactions. From our experimental results, zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Ni a Pi sample showed an advantage over Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Co a The hydrogen production activity of Pi sample is actually Ni a Ni produced by Pi transformation a P is a radical superior to Co a P as hydrogen-generating promoter. As is known, nickel phosphide catalysts are widely used as hydrogen production promoters due to their metalloid characteristics, and are applied to the photocatalytic hydrogen production half reaction of a sacrificial agent system, but are still rare in the application of photocatalytic decomposition of pure water to produce hydrogen. To our surprise, (Zn) a Cd b Mn c )S/(Zn d Mn e )S/PO x /Ni f Pi and (Zn) a Cd b Fe e )S/(Zn d Fe e )S/PO x /Ni f Pi bimetallic modified catalytic systems all show superiority to Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x /Ni a Pi hydrogen production activity. Fe added due to the simultaneous presence of metal ion exchange in the second step of the photosynthesis 3+ Or Mn 2+ Will be doped with Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Iron sulfide or manganese sulfide is formed in the material and loaded on the surface layer of the catalyst, and the sulfide catalyst promoters are easy to partially oxidize Fe in the process of decomposing pure water by photocatalysis x O or Mn x O。
TABLE 4 hydrogen generation rate table of catalyst after metal modification
Figure BSA0000253708240000071
Figure BSA0000253708240000081
Due to (Zn) d Fe e ) The S component has a wider band gap value, resulting in (Zn) a Cd b Fe c ) S and (Zn) d Fe e ) S two components easily form type I heterostructure type, but ZnS (DETA) 0.5 Materials of this kind tend to have a large number of defect structures, formed by cation exchange (Zn) d Fe e ) S material, also has defect energy level, so that (Zn) is in a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Internal to Pi catalytic system (Zn) a Cd b Fe c )S/(Zn d Fe e ) A quasi-type II heterostructure type is formed among the S components, and separation and transmission of photogenerated carriers in the heterostructure are facilitated. Therefore, in the application of photocatalytic decomposition of pure water, when visible light is irradiated to (Zn) a Cd b Fe c )S/(Zn d Fe e )S/PO x /Ni f Internal to the catalyst after Pi catalytic system a Cd b Fe c ) S and (Zn) d Fe e ) The S component is excited simultaneously in (Zn) a Cd b Fe c )S/(Zn d Fe e ) S heterojunctionIn the structure, photo-generated electrons and holes in the material are finally gathered to (Zn) a Cd b Fe c ) S conduction band sum (Zn) d Fe e ) In the defect energy level of S, the diethylenetriamine molecules complexed on the surface layer of the catalytic system can further transfer photoproduction holes to the surface layer, and finally the photoproduction holes can be Fe x O or Mn x O、Ni a Pi and other promoters are used for capturing to further improve the capture rate of photoproduction holes of the system, and in addition, the promoters and the phosphorus oxide protective layer can improve the anti-light corrosion capability of the system and indirectly improve the photocatalytic hydrogen production activity of the system; at the same time Ni a Partial conversion of Pi to Ni a P can capture photo-generated electrons and take the photo-generated electrons as sites to carry out proton reduction reaction to generate H 2 . Different types of cocatalysts are utilized to synergistically optimize the surface kinetic reaction rate of the catalytic system, so that the efficient and stable photocatalytic pure water decomposition process is realized.

Claims (3)

1. A preparation method of a catalyst for decomposing pure water by photocatalysis is characterized by comprising the following steps:
(1)Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 the heterojunction material is dispersed in H 2 PO 2 - In the solution, carrying out ultrasonic treatment under the protection of inert gas; said Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 The preparation of the heterojunction material comprises the following steps: weighing 315ml of diethylenetriamine and 35ml of pure water, mixing and pouring into a 500ml big beaker, weighing 1100mg of zinc acetate, 1322.5mg of cadmium acetate and 2450mg of L-cysteine, pouring into the beaker filled with the mixed solution, dissolving each medicine in the beaker by a magnetic stirrer and an ultrasonic cleaner, pouring the dissolved solution into a reaction kettle after each medicine is dissolved, screwing the reaction kettle, putting the reaction kettle into an electric heating constant temperature blast drying box for reacting for 24 hours at 180 ℃, and after the reaction is stopped, using a centrifuge to prepare Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Recovering and putting into an oven for dehydration to obtain yellow powder Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 A material;
(2) Then transferring the suspension obtained in the step (1) into a photocatalytic reactor, sealing the container, vacuumizing the whole reaction system by using a vacuum pump, irradiating the reactor by using a visible light source, and keeping the temperature at room temperature and stirring continuously;
(3) After the reaction is finished, opening the reactor, removing supernatant, centrifugally recovering precipitate, drying in an oven and recovering to obtain phosphate radical modified Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 Marked as Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x
(4) Taking Zn 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Sample, dispersed in H containing one or more transition metal salts 2 PO 2 - Ultrasonic treating in water solution under the protection of inert gas, transferring to a photocatalytic reactor, sealing the container, vacuumizing the whole reaction system by using a vacuum pump, irradiating the reactor by using a visible light source, keeping the temperature at room temperature, continuously stirring, opening the reactor after the reaction is finished, removing supernatant, centrifugally recovering precipitate, drying in an oven, and recovering to obtain Zn doped with transition metal 0.3 Cd 0.7 S/ZnS(DETA) 0.5 /PO x Namely the catalyst for decomposing pure water by photocatalysis;
the one or more transition metal salts are selected from nickel salts, cobalt salts, iron salts, mixed salts of nickel and iron, and mixed salts of nickel and manganese.
2. The production method according to claim 1,
the inert gas is nitrogen, argon or helium;
said H 2 PO 2 - The solution is NaH 2 PO 2 、KH 2 PO 2 One of (a) and (b);
the ultrasonic treatment time is 20-60min;
the vacuum treatment time is 10-30min;
the visible light source is one of sunlight, a xenon lamp, a mercury lamp, an incandescent lamp and a light-emitting diode lamp, and the processing time is 2-5h;
the drying temperature of the oven is 50-70 ℃, and the drying time is 10-15h.
3. A catalyst for photocatalytic decomposition of pure water prepared as described in claim 1 or 2.
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