CN114534746B - Photocatalytic hydrogen production system based on heterojunction photocatalyst and formaldehyde aqueous solution - Google Patents

Photocatalytic hydrogen production system based on heterojunction photocatalyst and formaldehyde aqueous solution Download PDF

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CN114534746B
CN114534746B CN202210196473.8A CN202210196473A CN114534746B CN 114534746 B CN114534746 B CN 114534746B CN 202210196473 A CN202210196473 A CN 202210196473A CN 114534746 B CN114534746 B CN 114534746B
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heterojunction
hydrogen production
hydrogen
oxygen
heterojunction photocatalyst
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CN114534746A (en
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闫晓庆
彭正鑫
李仁宏
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Zhejiang Sci Tech University ZSTU
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/39—Photocatalytic properties
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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
    • 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
    • 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
    • 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
    • B01J27/051—Molybdenum
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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
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    • 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
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/323—Catalytic reaction of gaseous or liquid organic compounds other than hydrocarbons with gasifying agents
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Abstract

The invention relates to the field of hydrogen energy, and discloses a photocatalysis hydrogen production system based on a heterojunction photocatalyst and formaldehyde aqueous solution, which comprises the heterojunction photocatalyst, oxygen and formaldehyde aqueous solution; the heterojunction photocatalyst is formed by compounding metal oxide and metal sulfide. The method for preparing hydrogen by utilizing the heterojunction photocatalyst and controlling the pressure or concentration of oxygen is characterized by controlling the formaldehyde aqueous solution to prepare hydrogen, wherein the oxygen is used as a cocatalyst in the reaction process without consumption or generation.

Description

Photocatalytic hydrogen production system based on heterojunction photocatalyst and formaldehyde aqueous solution
Technical Field
The invention relates to the field of hydrogen energy, in particular to a photocatalytic hydrogen production system based on a heterojunction photocatalyst and formaldehyde aqueous solution.
Background
It is well known that human beings survive and develop independently of energy. From the time when human beings enter industrialized age, energy and resources are increasingly in shortage, traditional fossil energy sources represented by coal, petroleum and natural gas are finally exploited, the irreproducibility of the traditional fossil energy sources brings more and more serious test to human survival and development, and a series of environmental pollution problems are increasingly aggravated due to the large-scale use of the fossil fuels.
With the development of socioeconomic and scientific technologies, people are paying more attention to energy and environmental problems, and development and research on green and renewable new energy are urgently needed to alleviate the current crisis. The development of clean and efficient new energy sources and the solving of the problems of energy shortage and environmental pollution gradually become the core mission of the development of the current society. The hydrogen has high combustion value, is nontoxic and odorless, and the combustion products are environment-friendly, thus being renewable energy sources. Hydrogen energy is playing an important role in meeting future sustainable energy demands in the world.
The most abundant hydrogen-containing material on earth is water, and next is various fossil fuels, coal, petroleum, natural gas, various biomasses, and the like. To utilize hydrogen energy, it is necessary to first develop a hydrogen source, i.e., to research and develop various methods of producing hydrogen. The hydrogen is prepared by taking water or biomass as raw materials in the long term, the raw materials are inexhaustible, and the hydrogen is combusted to release energy to generate product water, so that the environmental pollution is avoided.
The exploration of new renewable and clean energy sources has become an unprecedented reality problem, a great number of new energy development v has become a current hot spot, such as solar energy, wind energy, etc., and these energy sources become ideal substitutes for traditional fossil fuels due to their low cost, high benefit, environmental friendliness, etc., especially the direct conversion of solar energy into hydrogen fuel is considered as an effective measure for alleviating the current energy crisis and solving the environmental problem. The solar energy is an inexhaustible and green pollution-free new energy source, and has great potential for replacing the traditional energy source. First use of TiO since 1972 2 The original work of photocatalytic decomposition of the water to produce hydrogen is realized, and H is generated by photocatalytic water reduction 2 Has attracted considerable attention from researchers.
The photodecomposition of water to produce hydrogen is one of the methods which are widely researched, widely applied and mature at present. Water itself is a very stable compound, and the decomposition of water requires a large amount of energy, is a process of increasing gibbs free energy, is a process of raising energy barrier in the photocatalytic reaction, and is not spontaneously reacted. The photocatalytic degradation is a process of reducing the free energy of Gibbs, and belongs to a process of reducing the energy barrier in the photocatalytic reaction, so that the photocatalytic degradation is easier to occur than the reaction of producing hydrogen by photocatalysis water. From the thermodynamic aspect, according to formula H 2 O(l)→H 2 (g)+1/2O 2 (g)，The separation of 1mol of water into hydrogen and oxygen under standard conditions requires 285.5KJ of energy, and this reaction with an elevated energy barrier is thermodynamically difficult to occur. Theoretically, from an electrochemical point of view, the decomposition voltage of water is 1.23eV, and when the energy in the electric field is equal to or higher than 1.23eV, water can be decomposed. Therefore, in order to decompose water, the electron energy obtained from light by water must be greater than 1.23eV, in other words, the condition that the semiconductor used to promote water decomposition first satisfies as a photocatalyst is that the forbidden bandwidth is greater than 1.23eV. The conduction and valence bands of the semiconductor and the redox potential of water also have an effect on hydrogen and oxygen production.
In the field of photocatalytic hydrogen production, it is pointed out that the individual metal oxides or metal sulfides often face the problem of high carrier recombination rate during the photocatalytic reaction, which directly leads to a reduction in the photocatalytic hydrogen production efficiency. However, the method for compounding different semiconductors together to form the heterojunction has extremely special performance in the development of photocatalysis engineering, plays an indispensable role in innovative artificial materials, and the formation of the heterojunction promotes the separation of photon-generated carriers in the photocatalyst, reduces the recombination rate and improves the utilization rate of the photon-generated carriers, thereby achieving the purpose of improving the hydrogen production efficiency. It is noted that when two semiconductors are combined to form an energy band structure with alternate gaps, when electrons with low reducibility and holes with low oxidability are combined, electrons with high reducibility and holes with high oxidability are left to participate in the reaction, so that a Z-scheme type heterojunction is formed, the heterojunction can effectively separate electrons and holes, the oxidation-reduction capability of the catalyst can be improved, and the catalyst has more excellent performance.
It is well known that the organic matter has rich low carbon molecular resource, is important renewable energy source and has the characteristic of low oxidation reaction energy barrier. If the low-carbon organic molecule oxidation reaction can be used for replacing the traditional photo-electric decomposition water oxygen evolution reaction, the anode reaction potential can be reduced, and the overall energy conversion efficiency can be improved. Among the numerous low-carbon small organic molecules, formaldehyde (HCHO) solution is liquid at normal temperature, and the theoretical hydrogen content is as high as 8.4wt percent, which is far higher than that of formic acid (4.4 wt percent) widely used at present, so that the formaldehyde (HCHO) solution is favored by a large number of researchers as a hydrogen storage material. The formaldehyde and the water are simultaneously converted under mild reaction conditions to generate the hydrogen, so that the problem of high energy consumption of the traditional hydrogen production by photodecomposition of water is solved undoubtedly, and the large-scale combination and application of the hydrogen production by photodecomposition of water and renewable energy are facilitated.
Disclosure of Invention
Aiming at the defects of the prior art, the technical problem to be solved by the invention is to provide a low-energy-consumption even energy-consumption-free green catalytic hydrogen production system, in particular to a heterojunction photocatalyst-based and formaldehyde aqueous solution photocatalytic hydrogen production system, which utilizes the heterojunction photocatalyst to control the formaldehyde aqueous solution to produce hydrogen by controlling the pressure or concentration of oxygen, and oxygen is not consumed and generated as a cocatalyst in the reaction process.
The specific technical scheme of the invention is as follows: a photocatalysis hydrogen production system based on heterojunction photocatalyst and formaldehyde aqueous solution comprises heterojunction photocatalyst, oxygen and formaldehyde aqueous solution; the heterojunction photocatalyst is formed by compounding metal oxide and metal sulfide.
The invention develops a high-efficiency low-temperature photocatalytic hydrogen production system aiming at the problems that the hydrogen production activity is small, an additional noble metal cocatalyst is needed, the reaction temperature is high, the energy consumption is high, the process is complex, the conversion efficiency is low, byproducts are harmful, the hydrogen production efficiency is reduced along with the increase of the oxygen pressure or concentration (because the water decomposition hydrogen production reaction is a reversible reaction) and the like in the traditional hydrogen production reaction process, which are unfavorable for industrial application. The heterojunction photocatalyst can be used for preparing hydrogen by photocatalysis of formaldehyde aqueous solution, and oxygen is used as a cocatalyst in the hydrogen preparation process. The hydrogen element in the hydrogen generated by the photocatalysis hydrogen production system of the invention is derived from not only hydrogen in water, but also hydrogen in formaldehyde molecules as a sacrificial reagent. Under the action of formaldehyde molecules, oxygen and water molecules firstly generate active oxygen species (including peroxy free radical species and superoxide free radical species) on the surface of the heterojunction photocatalyst, and the active oxygen species can react with low-carbon small organic molecules to generate hydrogen and other byproducts such as acid, salt, carbon dioxide and the like.
The invention realizes the effect of preparing hydrogen by decomposing water with the heterojunction photocatalyst by utilizing the formaldehyde aqueous solution, and the heterojunction photocatalyst formed by compounding the metal oxide and the metal sulfide realizes high-performance hydrogen production by sharing metal atoms, and oxygen is not consumed and generated as a cocatalyst in the reaction process. Meanwhile, the catalyst system can be used in the fields of hydrogen production, energy chemical industry, hydrogen fuel cells, hydrogen-containing water preparation and the like.
The applicant finds that the hydrogen production efficiency and hydrogen production capacity of the photocatalytic hydrogen production system are controlled in proportion to oxides and sulfides in the heterojunction photocatalyst, and specifically the hydrogen production efficiency of the catalytic system is increased along with the increase of the content of the oxides in the heterojunction photocatalyst, wherein the content of the oxides is mainly obtained by the ratio of the crystallinity of the oxides to the crystallinity of the sulfides. In the heat treatment process, the crystallinity of the oxide gradually increases along with the increase of the heat treatment temperature, and the crystallinity of the sulfide shows a trend of increasing and then decreasing, and the ratio of the oxide to the sulfide in the heterojunction photocatalyst shows a trend of increasing and then decreasing, which directly influences the hydrogen production efficiency of the heterojunction photocatalyst.
It has been found more surprisingly that the hydrogen production efficiency of the photocatalytic hydrogen production system of the present invention is related to the oxygen content in the system at the same time, in particular, the hydrogen production efficiency of the photocatalytic hydrogen production system increases with the increase in the oxygen pressure or concentration in the reaction system at the initial stage of the reaction, wherein the amount of oxygen comprises the amount of oxygen in the gas phase and the dissolutionThe amount of oxygen in the water. The amount of oxygen dissolved in water is proportional to the amount of oxygen in the gas phase, according to Henry's law, especially at room temperature, the ratio is about 769.2 l.atm/mol. This oxygen-controlled hydrogen production is in contrast to the reverse reaction between oxygen and hydrogen, i.e. 2H 2 +O 2 →2H 2 O, generally in the presence of oxygen, the rate or amount of hydrogen production will decrease with increasing amounts of oxygen, while the hydrogen production efficiency of the photocatalytic hydrogen production system of the present invention will increase with increasing amounts of oxygen.
Preferably, the heterojunction photocatalyst is selected from In 2 O 3 /In 2 S 3 ，In 2 O 3 /Cr 2 S 3 And In 2 O 3 /MoS 2 The method comprises the steps of carrying out a first treatment on the surface of the Most preferably In 2 O 3 /In 2 S 3 。
The heterojunction type of the heterojunction photocatalyst is type-I, type-II, type-III or Z-scheme type, and most preferably Z-scheme type.
The Z-scheme type heterojunction can utilize a special electron transfer path thereof to enable electron holes to be effectively separated and increase the redox capability of a semiconductor. Compared with type-I heterojunction, both electrons and holes are accumulated on the same semiconductor with low oxidation and low reduction, and electron-hole pairs cannot be separated sufficiently effectively. In addition, the oxidation-reduction reactions on the type-I heterojunction all occur on semiconductors with low oxidation-reduction potentials, and the oxidation-reduction capability of the heterojunction photocatalyst is remarkably reduced. For type-II heterojunction, the electron transfer direction is from high reduction potential to low reduction potential, the hole transfer path is from high oxidation potential to low oxidation potential, and the space separation of electron-hole pairs is realized, but high oxidation-reduction capability cannot be realized at the cost of reducing the oxidation-reduction capability of the semiconductor heterojunction. In summary, the Z-scheme heterojunction not only realizes the effective separation of electrons and holes, but also increases the oxidation-reduction capability of the catalyst.
Preferably, the heterojunction photocatalyst has a shape of a particle, sphere, rod, line, tube, chain, cube, octahedron, flower or hydrangea. Further, a flower shape or a hydrangea shape is preferable.
Preferably, the molar ratio of the metal oxide to the metal sulfide in the heterojunction photocatalyst is (0.5-2) to 1;
preferably, the sizes of the metal oxide and the metal sulfide in the heterojunction photocatalyst are 5-6 mu m.
Furthermore, the photocatalytic hydrogen production system does not need to add extra auxiliary agents, but does not exclude the addition of auxiliary agents to the reaction system to improve the reaction rate, wherein the auxiliary agents are selected from KOH, naOH, K 2 CO 3 、Na 2 CO 3 Any one or any plurality of the above.
Further, the team of the present invention found that formaldehyde molecules in formaldehyde solutions readily formed water into methylene glycol (hcho+h) 2 O→CH 2 (OH) 2 ) The hydroxide ion in the selected basic auxiliary agent can abstract hydrogen (CH) on the hydroxyl of the methyl glycol 2 (OH) 2 +OH-→CH 2 (OH)O-+H 2 O), promotes the dehydrogenation reaction of formaldehyde molecules, thereby improving the hydrogen production reaction rate.
Preferably, the concentration of the heterojunction photocatalyst in the hydrogen production system is 2-8 g/L;
preferably, the formaldehyde solution has a low concentration (0-1M) and a high concentration (1-4M);
preferably, the pressure of the oxygen is 0 to 0.10 megapascals.
Preferably, the heterojunction photocatalyst is loaded in a carrier; the carrier is an organic or inorganic substance with a loading function. Including but not limited to ceramics, glass, fibers, cloth, plastics, paint, molecular sieves.
Preferably, the preparation of the heterojunction photocatalyst comprises the following steps:
1) Preparing metal oxide, and controlling morphology by adding surfactant;
2) And (3) carrying out hydrothermal in-situ growth of metal sulfide on the surface of the metal oxide prepared in the step (1) to prepare a composite photocatalyst, and then stabilizing by a heat treatment method and removing pollutants on the surface of the material to obtain the heterojunction photocatalyst.
Preferably, the surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium dodecyl alcohol polyoxyethylene ether sulfate, ammonium dodecyl sulfate and triethanolamine lauryl sulfate. Preferably sodium lauryl sulfate.
Preferably, the photocatalysis hydrogen production system can be applied to hydrogen production, energy chemical industry, batteries and hydrogen-containing water preparation. Furthermore, the hydrogen prepared by the catalytic system can be used as a high-quality fuel in the energy chemical process. Further, the catalyst may be prepared as an electrode for a battery. Still further, the catalytic system may be used in the medical field, such as in the preparation of medical hydrogen-containing water.
Compared with the prior art, the invention has the following technical effects:
1) The photocatalysis hydrogen production system has high hydrogen production efficiency, low price and easy obtainment of raw materials, clean and environment-friendly catalysis process, no harm to environment and human body and capability of carrying out waste utilization on aldehyde-containing wastewater and waste gas. Meanwhile, the hydrogen element in the prepared hydrogen is derived from formaldehyde and water; in view of the fact that formaldehyde molecules and water are renewable raw materials, the catalytic process is a sustainable hydrogen production method and is suitable for industrial production;
2) The heterojunction photocatalyst used in the photocatalytic hydrogen production system constructs a Z-schema heterojunction in the body, utilizes a special electron transfer path thereof to effectively separate electron holes, increases the oxidation-reduction capability of a semiconductor, and combines low-reducibility electrons and low-oxidability holes in the heterojunction photocatalyst to enable high-reducibility electrons and high-oxidability holes to be utilized, thereby improving the hydrogen production performance;
3) Compared with the traditional photocatalytic hydrogen production system, the photocatalytic hydrogen production system has special effects. The presence of oxygen in conventional hydrogen production systems has a negative effect on hydrogen production, as the yield and rate of hydrogen decreases with increasing oxygen pressure or concentration in the system; the oxygen plays a role of a promoter in the hydrogen production process, and the yield and the rate of the hydrogen can be increased along with the increase of the oxygen pressure or the concentration in the system; the oxygen raw material is easy to obtain, has wide sources, is safe and reliable, is an inexpensive cocatalyst, and can be effectively utilized;
4) The invention can be extended to the field of environmental purification treatment, in particular to decomposition and harmless treatment of formaldehyde;
5) The catalytic system related by the invention can be used in the fields of hydrogen production, energy chemical industry, hydrogen fuel cells, hydrogen-containing water preparation and the like.
Drawings
FIG. 1 is In 2 O 3 /In 2 S 3 XRD spectra, SEM pictures, HR-TEM pictures and mapping pictures of the heterojunction.
FIG. 2 is In 2 O 3 SEM pictures of the catalyst.
FIG. 3 is In 2 O 3 、In 2 S 3 And In 2 O 3 /In 2 S 3 The heterojunction catalyzes the effect of formaldehyde solution hydrogen production.
FIG. 4 is an In heat treated at different temperatures 2 O 3 /In 2 S 3 The heterojunction catalyzes the effect of formaldehyde solution hydrogen production.
FIG. 5 shows oxygen partial pressure (low pressure) vs. In 2 O 3 /In 2 S 3 Heterojunction catalyzes the effect of formaldehyde solution hydrogen production.
FIG. 6 is a double logarithmic graph showing In at the previous hour 2 O 3 /In 2 S 3 The catalytic activity of the heterojunction catalyst is proportional to the partial pressure of oxygen.
FIG. 7 is In 2 O 3 /In 2 S 3 The heterojunction catalyzes the change of oxygen concentration in the process of the formaldehyde solution hydrogen production reaction.
FIG. 8 is a different method of preparing In 2 O 3 /In 2 S 3 The heterojunction catalyst catalyzes the effect of formaldehyde solution hydrogen production.
FIG. 9 is a graph of formaldehyde concentration versus In 2 O 3 /In 2 S 3 Heterojunction catalyzes the effect of formaldehyde solution hydrogen production.
FIG. 10 is a graph of sodium hydroxide vs. In 2 O 3 /In 2 8 3 Heterojunction catalyzes the effect of formaldehyde solution hydrogen production.
FIG. 11 is In 2 O 3 /In 2 S 3 PL spectrum of heterojunction.
FIG. 12 is In 2 O 3 /In 2 S 3 Fluorescence lifetime plot of heterojunction.
FIG. 13 is In 2 O 3 /In 2 S 3 Transient photoelectric diagram of heterojunction.
FIG. 14 is In 2 O 3 /In 2 S 3 Impedance diagram of heterojunction.
FIG. 15 is In 2 O 3 /In 2 S 3 Energy band structure diagram of heterojunction.
Detailed Description
The invention is further described below with reference to examples.
Example test method: 10 mg of In was taken 2 O 3 /In 2 S 3 The catalyst is put into 5 ml of formaldehyde aqueous solution with the concentration of 1mol/L, the reaction temperature is set to be 25 ℃ at normal temperature, and the reaction solution is stirred under the air atmosphere (the partial pressure of oxygen is about 0.21 atm; atm is the standard atmospheric pressure, namely 0.101 MPa), H 2 Is continuously produced from aqueous solution, and H 2 The production rate of (C) was 6.9 mmol/h.g, wherein the unit mmol/h.g means the amount of hydrogen produced per gram of catalyst per hour (millimoles).
Wherein the partial pressure of oxygen and the amount of hydrogen produced were measured by GC-TCD (gas chromatography packed column by Porapak Q column or 5A molecular sieve column), and the product in the liquid phase was measured by GC-MS. All examples and comparative examples of the present invention were used to determine gas content and liquid product by this method.
Example 1
In molar ratio of 1:1 2 O 3 /In 2 S 3 The morphology and structural characterization of the heterojunction catalyst is shown in fig. 1. FIG. 1a shows In heat treated at various temperatures (400-700 ℃ C.) 2 O 3 /In 2 S 3 XRD pattern of heterojunction containing In 2 O 3 And In 2 S 3 Diffraction peaks of (1) to show In 2 O 3 And In 2 S 3 Coexisting in the catalyst; FIG. 1b is an In heat treated at 500 ℃ 2 O 3 /In 2 S 3 The heterojunction SEM picture shows that the appearance of the heterojunction SEM picture is an embroidered ball-shaped structure; FIG. 1c is an In heat treated at 500 ℃C 2 O 3 /In 2 S 3 HR-TEM pictures of heterojunction showing In 2 O 3 (111) Crystal plane and In 2 S 3 (200) A crystal plane; FIG. 1d is an In heat treated at 500 DEG C 2 O 3 /In 2 S 3 Mapping graph of heterojunction showing In 2 O 3 /In 2 S 3 In, O and S three elements In the heterojunction are uniformly distributed. In (In) 2 O 3 /In 2 S 3 Heterojunction catalyst is prepared by reacting In 2 O 3 Is prepared by In-situ vulcanization treatment, in 2 O 3 /In 2 S 3 The heterojunction catalyst has the morphology source of In 2 O 3 Loading In on flower-like structure 2 S 3 Formed, FIG. 2 shows In 2 O 3 Is a flower-like structure. XRD refers to X-ray diffraction, SEM refers to scanning electron microscopy, HR-TEM refers to high power transmission electron microscopy, mapping is elemental mapping.
Examples 2 to 4
10 mg of In was taken 2 O 3 (example 2), in 2 S 3 Example 3 and In 2 O 3 /In 2 S 3 Heterojunction (example 4, which is In prepared by In situ sulfidation, followed by 500 ℃ C. Heat treatment) 2 O 3 And In 2 S 3 Heterojunction with mol ratio of 1:1, hydrangea shape, and 5 ml of formaldehyde water solution with concentration of 1mol/L are respectively placed into the heterojunction, the reaction temperature is set to be normal temperature 25 ℃, the reaction solution is stirred under the air atmosphere (oxygen partial pressure is about 0.21 atm), and H 2 Continuously from aqueous solutions.
In as shown In Table 1 and FIG. 3 2 O 3 /In 2 S 3 The hydrogen production rate of the heterojunction is significantly higher than In 2 O 3 And In 2 S 3 Is In 2 O 3 166 times of In 2 S 3 Is 6 times as large as that of the above. Shows In prepared In the hydrogen production system 2 O 3 /In 2 S 3 The hydrogen production rate of the heterojunction is obviously higher than that of pure substances, and the heterojunction has obvious enhancement effect on catalyzing the hydrogen production of formaldehyde aqueous solution, because the formed Z-schema type heterojunction can effectively separate electrons and holes in the catalytic reaction process, has higher oxidation-reduction performance, and can efficiently catalyze the hydrogen production of formaldehyde solution.
Table 1 (data of FIG. 3)
Sequence number The material used 6h Hydrogen formation per micromolar
Example 2 In 2 O 3 2.37
Example 3 In 2 S 3 64.28
Example 4 In 2 O 3 /In 2 S 3 Heterojunction structure 393.42
Examples 5 to 8
Examples 5-8 study on In In Hydrogen production System 2 O 3 /In 2 S 3 Heterojunction (the heterojunction is hydrangea-shaped In prepared by an In-situ vulcanization method) 2 O 3 /In 2 S 3 Heterojunction with a molar ratio of 1:1) heat treated at different temperatures (400, 500, 600, 700 ℃ C.) to In 2 O 3 /In 2 S 3 Heterojunction catalyzes the effect of formaldehyde aqueous solution hydrogen production. Reaction conditions: at room temperature (25 ℃ C.), the formaldehyde concentration is 1mol/L, the volume is 5 ml, and In 2 O 3 /In 2 S 3 The mass is 10 mg; for the reactions of examples 5-8, the reaction time was 6 hours.
As can be seen from the data of examples 5 to 8 In Table 2 and FIG. 4, the hydrogen production amount increases and decreases after 6 hours with the gradual increase of the calcination temperature, which shows that the calcination temperature has a certain effect on the hydrogen production performance, and the XRD pattern of FIG. 1a shows that the temperature has a certain effect on In 2 O 3 /In 2 S 3 In heterojunction 2 O 3 And In 2 S 3 The crystallinity and the content are affected, which means that different temperatures are achieved by affecting In 2 O 3 And In 2 S 3 Crystallinity and content, and further influence the hydrogen production of formaldehyde by catalysis.
Table 2 (data of FIG. 4)
Examples 9 to 18
Examples 9-18 investigate different oxygen pressure/concentration vs. In hydrogen production systems 2 O 3 /In 2 S 3 Heterojunction (the heterojunction is prepared by an In-situ vulcanization method, and is subjected to heat treatment at 500 ℃ to obtain In 2 O 3 And In 2 S 3 Heterojunction with a molar ratio of 1:1 and a shape of hydrangea) catalyzes the influence of formaldehyde aqueous solution hydrogen production. Reaction conditions: at room temperature (25 ℃ C.), the formaldehyde concentration is 1mol/L, the volume is 5 ml, and In 2 O 3 /In 2 S 3 The mass is 10 mg; for the reactions of examples 9-18, the reaction time was 1 hour.
From the data of examples 9-18 in Table 3 and FIG. 5, it can be seen that when the oxygen pressure is 0 (example 9), there is little hydrogen production, and when the oxygen pressure is increased from 0.00 to 0.100 megapascals, the hydrogen production increases, indicating that oxygen has a decisive influence on hydrogen production. At the same time, by controlling the oxygen pressure, we can also control the rate and total amount of hydrogen production. As can be seen from FIG. 5, in 2 O 3 /In 2 S 3 In the process of preparing hydrogen by catalyzing formaldehyde solution through heterojunction, along with the increase of partial pressure of oxygen, the hydrogen generation rate is also increased. It can also be seen from FIG. 5 that In 2 O 3 /In 2 S 3 In the process of preparing hydrogen by using the formaldehyde solution through heterojunction catalysis, the partial pressure of oxygen plays a vital role, and when the partial pressure of oxygen is increased from low pressure (0 at the minimum) to normal pressure and finally to high pressure (1.0 megapascal), the hydrogen generation amount in unit time is always increased. Meanwhile, we found that the hydrogen production activity of the catalyst is proportional to the oxygen partial pressure after making a double logarithmic curve of the hydrogen production activity and the oxygen partial pressure of the catalyst (fig. 6). As can be seen from FIG. 6, in within the range of the oxygen partial pressure (0.about.0.1 MPa) verified 2 O 3 /In 2 S 3 The hydrogen production rate of the heterojunction catalytic formaldehyde solution is proportional to the partial pressure of oxygen.
Table 3 (data of FIG. 5)
Examples 19 to 22
Preparation of In by comparison of different methods 2 O 3 /In 2 S 3 Heterojunction catalysis formaldehyde aqueous solution hydrogen production effect. The method comprises the following steps: direct sulfidation of flower-like In 2 O 3 /In 2 S 3 Heterojunction (DS-HOS) is prepared by mixing and grinding hydrothermal indium oxide and sulfur powder according to a mass ratio of 1:1, placing the mixture in a tube furnace, calcining the mixture for 25min at a temperature rising rate of 500 ℃ under a hydrogen-argon atmosphere, and rapidly cooling the mixture to collect a sample. The second method is as follows: in situ sulfidation of particulate In 2 O 3 /In 2 S 3 Heterojunction (IS-POS) IS obtained by ultrasonically dispersing 250 mg of particulate indium oxide in 80 ml of deionized water, then adding 125 mg of thioacetamide, placing into an autoclave, and vulcanizing at 150 ℃ for 5 hours. And a third method: direct grinding of In 2 O 3 /In 2 S 3 The heterojunction (DS-GOS) is obtained by fully mixing and grinding flower-shaped indium oxide and indium sulfide according to the mol ratio of 1:1. The method four: in-situ sulfuration flower-like In used In the hydrogen production system 2 O 3 /In 2 S 3 Heterojunction (IS-HOS) IS obtained by ultrasonically dispersing 250 mg of flower-like indium oxide in 80 ml of deionized water, then adding 125 mg of thioacetamide, placing in an autoclave, and vulcanizing at 150 ℃ for 5 hours.
Taking In synthesized by four methods respectively 2 O 3 /In 2 S 3 The heterojunction 10 mg is put into 5 ml of aqueous solution of formaldehyde with concentration of 1mol/L, the reaction temperature is set to be 25 ℃ at normal temperature, the reaction solution is stirred under the atmosphere of air (the partial pressure of oxygen is about 0.21 atm), H 2 Is continuously generated from aqueous solution, H 2 The rate of generation of (2) is shown in table 4 and fig. 8.
As can be seen from Table 4 and FIG. 8, in was prepared by various methods 2 O 3 /In 2 8 3 The heterojunction catalyst can catalyze formaldehyde aqueous solution to prepare hydrogen, wherein, in-situ sulfuration flower-like In 2 O 3 /In 2 The hydrogen production efficiency of the S3 heterojunction is relatively highest, and In is directly ground 2 O 3 /In 2 The hydrogen production efficiency of the S3 heterojunction is relatively worst, and the total hydrogen production efficiency is arranged in the following order: in-situ sulfidation of flower-like In 2 O 3 /In 2 S 3 Heterojunction > In-situ vulcanized granular In 2 O 3 /In 2 S 3 Heterojunction approximately equal to direct sulfuration flower-like In 2 O 3 /In 2 S 3 Heterojunction approximately equal to direct grinding In 2 O 3 /In 2 S 3 And a heterojunction.
Table 4 (data of FIG. 8)
Sequence number Preparation method Short for short 6h Hydrogen formation per micromolar
Example 19 Directly vulcanizing flower shape DS-HOS 18.79
Example 20 In situ vulcanized particulate IS-POS 42.82
Example 21 Direct grinding DS-GOS 4.8
Example 22 In situ sulfidation of flower shape IS-HOS 96.8
Example 23
10 mg of In was taken 2 O 3 /In 2 S 3 Heterojunction catalyst (In prepared by In situ sulfuration method and heat-treated at 500℃) 2 O 3 And In 2 S 3 Heterojunction with molar ratio of 1:1, and in the shape of hydrangea), placing into 5 ml of formaldehyde water solution with concentration of 1mol/L, setting reaction temperature at normal temperature 25 ℃, stirring reaction solution under air atmosphere (oxygen partial pressure about 0.21 atm), and researching O in gas phase 2 、H 2 Is a trend of change in (c). As can be seen from FIG. 7, in 2 O 3 /In 2 S 3 H in the process of hydrogen production by catalyzing formaldehyde aqueous solution through heterojunction 2 The amount of oxygen produced increases with time, while the oxygen content remains almost unchanged. This is demonstrated In 2 O 3 /In 2 S 3 In the process of catalyzing formaldehyde to prepare hydrogen by the heterojunction, oxygen plays a role of an auxiliary catalyst.
Examples 24 to 32
10 mg of In was taken 2 O 3 /In 2 S 3 Heterojunction catalyst (In prepared by In situ sulfuration method and heat-treated at 500℃) 2 O 3 And In 2 S 3 Heterojunction with the mol ratio of 1:1 and in the shape of hydrangea is placed into 5 milliliters of formaldehyde aqueous solution with different concentrations, the reaction temperature is set to be 25 ℃ at normal temperature, the reaction solution is stirred under the air atmosphere (the oxygen partial pressure is about 0.21 atm), and H2 is continuously generated from the aqueous solution.
As can be seen from Table 5 and FIG. 9, in 2 O 3 /In 2 S 3 In the process of preparing hydrogen by catalyzing formaldehyde aqueous solution through heterojunction, when formaldehyde concentration is less than 1mol/L, H 2 The production rate increases rapidly with increasing formaldehyde concentration; when the formaldehyde concentration is more than 1mol/L, H 2 The production rate gradually decreases with increasing formaldehyde concentration.
Table 5 (data of FIG. 9)
Sequence number Formaldehyde concentration/M 1h Hydrogen formation per micromole 6h Hydrogen formation per micromolar
Example 24 0 0.2 1.0
Example 25 0.2 61.5 116.8
Example 26 0.4 63.5 148.8
Example 27 0.6 75.7 160.4
Example 28 0.8 81.5 173.6
Example 29 1 105.4 265.9
Example 30 2 58.4 251.8
Example 31 3 33.0 142.0
Example 32 4 22.3 101.2
Examples 33 to 41
10 mg of In was taken 2 O 3 /In 2 8 3 Heterojunction catalyst (In prepared by In situ sulfuration method and heat-treated at 500℃) 2 O 3 And In 2 S 3 Heterojunction with a molar ratio of 1:1 and a shape of hydrangea) is placed into 5 ml of formaldehyde 1mol/L NaOH aqueous solution with different concentrations, the reaction temperature is set to be normal temperature 25 ℃, the reaction solution is stirred under the air atmosphere (oxygen partial pressure is about 0.21 atm), and H 2 Continuously from aqueous solutions.
As can be seen from Table 6 and FIG. 10, in 2 O 3 /In 2 S 3 In the process of preparing hydrogen by catalyzing formaldehyde aqueous solution through heterojunction, when NaOH concentration is less than 1mol/L, H 2 The production rate increases rapidly with increasing NaOH concentration; when the concentration of NaOH is more than 1mol/L, H 2 The rate of production gradually decreases with increasing NaOH concentration.
Table 6 (data of FIG. 10)
Sequence number NaOH concentration/M 1h Hydrogen formation per micromole 6h Hydrogen formation per micromolar
Example 33 0 0 0.3
Example 34 0.2 13.7 39.6
Example 35 0.4 23.9 138.9
Example 36 0.6 30.5 183.4
Example 37 0.8 54.9 187.0
Example 38 1 105.4 265.9
Example 39 2 64.0 196.9
Example 40 3 49.3 167.6
Example 41 4 42.9 153.5
From the above, examples 1 to 41 show that In 2 O 3 /In 2 S 3 The heterojunction catalyst has the following characteristics in the process of catalyzing aldehyde solution to prepare hydrogen:
1) Heat treatment of In at different temperatures 2 O 3 /In 2 S 3 Heterojunction pair In 2 O 3 And In 2 S 3 The crystallinity and the content of the catalyst have a certain influence, and the crystallinity and the content are influenced to further influence the hydrogen production rate, and the hydrogen production rate is increased and then decreased along with the increase of the heat treatment temperature;
2) The oxygen plays a role of a catalyst promoter in the catalytic hydrogen production process, namely, the higher the oxygen partial pressure or the oxygen concentration is, the faster the hydrogen production rate is, the higher the yield is, and meanwhile, the oxygen partial pressure is almost unchanged along with the reaction;
3) In prepared by In situ sulfidation flower-like method 2 O 3 /In 2 S 3 The heterojunction catalyst shows a significantly stronger hydrogen production rate In catalyzing formaldehyde solution to produce hydrogen than other methods, which indicates In prepared by the method 2 O 3 /In 2 S 3 The heterojunction is most favorable for electron-hole transfer in the heterojunction, reduces the recombination of electron-hole pairs and promotes the hydrogen production activity;
4)In 2 O 3 /In 2 S 3 the hydrogen production rate of the heterojunction catalyst for catalyzing formaldehyde to produce hydrogen is better than that of pure material In 2 O 3 And In 2 S 3 Is In 2 O 3 166 times of In 2 S 3 Is 6 times that of (2);
6)In 2 O 3 /In 2 S 3 the heterojunction catalyst can catalyze aldehyde solution to prepare hydrogen at room temperature;
7)In 2 O 3 /In 2 S 3 heterojunction catalysts can tolerate higher concentrations of aldehyde solutions to produce hydrogen, i.e., in high concentrations of aldehyde solutions (e.g., 4mol/L formaldehyde solution), in 2 O 3 /In 2 S 3 The heterojunction still maintains high hydrogen production efficiency;
8)In 2 O 3 /In 2 S 3 heterojunction catalysts can tolerate higher concentration NaOH solutions to produce hydrogen, i.e., in high concentration NaOH solutions (e.g., 4mol/L NaOH solution), in 2 O 3 /In 2 S 3 The heterojunction still maintains high hydrogen production efficiency.
Example 42
10 mg of In was taken 2 O 3 /In 2 S 3 (In prepared by In situ vulcanization and heat treatment at 500 ℃ C.) 2 O 3 And In 2 S 3 Heterojunction with mol ratio of 1:1, shape of hydrangea), in 2 O 3 /Cr 2 S 3 (In 2 O 3 /Cr 2 S 3 The heterojunction is prepared by hydrothermal method, and is subjected to heat treatment at 500 ℃ In nitrogen atmosphere to obtain In 2 O 3 And Cr (V) 2 S 3 Heterojunction with molar ratio of 1:1), in 2 O 3 /MoS 2 (In 2 O 3 /MoS 2 The heterojunction is prepared by hydrothermal method, and is subjected to heat treatment at 500 ℃ In nitrogen atmosphere to obtain In 2 O 3 And MoS 2 Heterojunction with a molar ratio of 1:1) heterojunction catalyst was placed in 5 ml of 1mol/L aqueous formaldehyde solution, the reaction temperature was set to 25 ℃ at ordinary temperature, and the reaction solution was stirred under an air atmosphere (oxygen partial pressure of about 0.21 atm) and H2 was continuously generated from the aqueous solution.
As shown In Table 8, in the comparison of the experiments for catalyzing the hydrogen production of formaldehyde solution 2 O 3 /In 2 S 3 、In 2 O 3 /Cr 2 S 3 、In 2 O 3 /MoS 2 The heterojunction photocatalyst has good catalytic hydrogen production activity, wherein the hydrogen production rate is In 2 O 3 /In 2 S 3 Optimally, in 2 O 3 /Cr 2 S 3 Next, in 2 O 3 /MoS 2 Worst. In (In) 2 O 3 /In 2 S 3 The reason for the highest activity is In 2 O 3 And In 2 S 3 The common metal In atoms play a role of a bridge at the heterojunction interface, and the electron and hole transfer rate of the heterojunction is improved, so that In 2 O 3 /In 2 S 3 Heterojunction activity is superior to other high-performance photocatalyst sulfides and In 2 O 3 The heterojunction formed.
TABLE 8
Catalyst 1h Hydrogen formation per micromole 6h Hydrogen formation per micromolar
In 2 O 3 /In 2 S 3 63.84 367.3
In 2 O 3 /Cr 2 S 3 40.6 231.1
In 2 O 3 /MoS 2 35.53 201.8
Example 43
Respectively taking a certain amount of In 2 O 3 /In 2 S 3 Heterojunction (In prepared by In situ sulfuration method and heat treatment at 500℃) 2 O 3 And In 2 S 3 Heterojunction with mol ratio of 1:1, shape of hydrangea), in 2 O 3 And In 2 S 3 PL spectrum testing was performed. PL spectra are reliable analyses that elucidate the carrier separation and transport efficiency. As shown In fig. 11, in 2 O 3 And In 2 S 3 The main strong emission peaks are around 405nm (excitation wavelength=350 nm) and 390nm (excitation wavelength=250 nm), indicating In 2 O3 and In 2 The light-induced electrons and holes of S3 will recombine rapidly and the utilization of electrons and holes will be greatly reduced. In (In) 2 O 3 And In 2 S 3 In formed after the compounding 2 O 3 /In 2 S 3 The PL intensity of the heterojunction is greatly reduced, in 2 O 3 /In 2 S 3 The heterojunction exhibits a very weak emission peak at the same location. The PL spectrum of the IS-HOS sample has a broad emission peak at 390nm, and IS matched with In 2 O 3 The band transition PL radiation under incident light corresponds to a DRS absorption edge approximately equal to In2O 3. The PL intensity of the 500IS-HOS sample was lower than 600IS-HOS, 700IS-HOS and 4The 00IS-HOS sample shows that heterojunction formed at 500 ℃ can enhance separation and transfer of photogenerated electrons and holes and weaken recombination of photogenerated electrons and holes. This is In with In 2 O 3 /In 2 S 3 The hydrogen production rate of the heterojunction catalytic formaldehyde solution is the same.
Example 44
Respectively taking a certain amount of In 2 O 3 /In 2 S 3 Heterojunction (In prepared by In situ sulfuration method and heat treatment at 500℃) 2 O 3 And In 2 S 3 Heterojunction with mol ratio of 1:1, shape of hydrangea), in 2 O 3 And In 2 S 3 Fluorescence lifetime testing was performed. The fluorescence lifetime of the catalyst is an important factor affecting the photocatalytic activity. As shown in FIG. 12, the average carrier emission lifetimes for 400IS-HOS, 500IS-HOS, 600IS-HOS, and 700IS-HOS heterojunction catalysts were 0.80, 1.06, 0.88, and 0.87ns, respectively. In (In) 2 O 3 /In 2 S 3 The average carrier lifetime of the heterojunction is significantly greater than that of pure material In 2 O 3 (0.69 ns) and In 2 S 3 (0.75 ns), further described In 2 O 3 /In 2 S 3 The heterojunction improves the carrier separation and the transfer efficiency between the heterojunction, and improves the hydrogen production activity of the catalytic formaldehyde solution. This is In with In 2 O 3 /In 2 S 3 The hydrogen production rate of the heterojunction catalytic formaldehyde solution is the same.
Example 45
Respectively taking a certain amount of In 2 O 3 /In 2 S 3 Heterojunction (In prepared by In situ sulfuration method and heat treatment at 500℃) 2 O 3 And In 2 S 3 Heterojunction with mol ratio of 1:1, shape of hydrangea), in 2 O 3 And In 2 S 3 Transient photocurrent testing was performed on a load and indium tin oxide slide using an electrochemical workstation. As shown in fig. 13, the transient photocurrent test was achieved by a 30 second optical switch. The photocurrent density of the catalyst increased sharply when the light source was turned on and then remained stable, indicating that these samples were acceptable for useThe light is very sensitive. In (In) 2 O 3 And In 2 S 3 Exhibit a lower photocurrent density, once In 2 O 3 And In 2 S 3 Composite formation of In 2 O 3 /In 2 S 3 Heterojunction with greatly increased current density, especially 500IS-HOS to maximum current density, compared to pure In 2 O3 is eighty times higher, showing that the formation of heterojunction leads to rapid transfer and separation of photogenerated charge. This is In with In 2 O 3 /In 2 S 3 The hydrogen production rate of the heterojunction catalytic formaldehyde solution is the same.
Example 46
Respectively taking a certain amount of In 2 O 3 /In 2 S 3 Heterojunction (In prepared by In situ sulfuration method and heat treatment at 500℃) 2 O 3 And In 2 S 3 Heterojunction with mol ratio of 1:1, shape of hydrangea), in 2 O 3 And In 2 S 3 Impedance testing was performed on a load and indium tin oxide slide using an electrochemical workstation. Normally, the smaller the arc radius in the high-frequency, low-resistance region, the higher the carrier separation efficiency. As shown In FIG. 14, the radius of the impedance arc of 500IS-HOS IS the smallest, and the semicircular diameter rule of all these samples IS 500IS-HOS < 600IS-HOS < 700IS-HOS < 400IS-HOS < In 2 S 3 ＜In 2 O 3 This illustrates In 2 O 3 /In 2 S 3 The construction of the heterojunction is beneficial to improving the utilization of photoexcitation state electrons and holes, thereby improving the efficiency of catalyzing formaldehyde to prepare hydrogen. This is In with In 2 O 3 /In 2 S 3 The hydrogen production rate of the heterojunction catalytic formaldehyde solution is the same.
Example 47
As shown In FIG. 15, in is plotted 2 O 3 And In 2 S 3 In 2 O 3 /In 2 S 3 The heterojunction forms an interleaved energy band. In (In) 2 O 3 The conduction band value of (2) is 0.53eV and the valence band value is 3.63eV. In (In) 2 S 3 The conduction band value of (2) is-0.79 eV and the valence band value is 1.21eV.
The raw materials and equipment used in the invention are common raw materials and equipment in the field unless specified otherwise; the methods used in the present invention are conventional in the art unless otherwise specified.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent transformation of the above embodiment according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.

Claims (3)

1. A photocatalytic hydrogen production system based on a heterojunction photocatalyst and an aqueous formaldehyde solution is characterized in that: comprises a heterojunction photocatalyst, oxygen, formaldehyde aqueous solution and auxiliary agent;
the heterojunction photocatalyst is formed by compounding In formed by metal oxide and metal sulfide with the mol ratio of (0.5-2): 1 2 O 3 /In 2 S 3 The method comprises the steps of carrying out a first treatment on the surface of the The heterojunction type is Z-scheme type; the shape is flower-shaped or hydrangea-shaped;
the auxiliary agent is selected from KOH, naOH, K 2 CO 3 And Na (Na) 2 CO 3 Any one or more of the following;
the concentration of the heterojunction photocatalyst in the hydrogen preparation system is 2-8 g/L; the concentration of the formaldehyde solution is 0.2-4M with low concentration; the pressure of the oxygen is 0.021-0.10 megapascals;
the heterojunction photocatalyst is prepared by an in-situ vulcanization method and comprises the following steps:
1) Preparing metal oxide, and controlling morphology by adding surfactant;
2) Performing hydrothermal in-situ growth of metal sulfide on the surface of the metal oxide prepared in the step 1) to prepare a composite photocatalyst, and then stabilizing by a heat treatment method, and removing pollutants on the surface of the material to obtain a heterojunction photocatalyst;
the surfactant is one or more selected from sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium dodecyl alcohol polyoxyethylene ether sulfate, ammonium dodecyl sulfate and triethanolamine lauryl sulfate.
2. The photocatalytic hydrogen production system as set forth in claim 1, wherein: the sizes of the metal oxide and the metal sulfide in the heterojunction photocatalyst are 5-6 mu m.
3. The photocatalytic hydrogen production system according to claim 1 or 2, characterized in that: the heterojunction photocatalyst is loaded in a carrier; the carrier is an organic or inorganic substance with a loading function.
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