FI128375B - Nanocomposites for photocatalytic water splitting using visible light and method for synthesis thereof - Google Patents

Nanocomposites for photocatalytic water splitting using visible light and method for synthesis thereof Download PDF

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FI128375B
FI128375B FI20185096A FI20185096A FI128375B FI 128375 B FI128375 B FI 128375B FI 20185096 A FI20185096 A FI 20185096A FI 20185096 A FI20185096 A FI 20185096A FI 128375 B FI128375 B FI 128375B
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water
nanocomposite
nickel
silver
nanocomposites
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FI20185096A
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Finnish (fi)
Swedish (sv)
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FI20185096A1 (en
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Xinying Shi
Wei Cao
Marko Huttula
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Wmz Nanosurfaces Oy
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Priority to PCT/FI2019/050069 priority patent/WO2019150000A1/en
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    • B01J35/39—
    • 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
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/66—Silver or gold
    • B01J23/68—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/683—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with chromium, molybdenum or tungsten
    • B01J23/686—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with chromium, molybdenum or tungsten with molybdenum
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/85—Chromium, molybdenum or tungsten
    • B01J23/88—Molybdenum
    • B01J23/883—Molybdenum and nickel
    • 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
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/892—Nickel and noble metals
    • 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
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8933—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/8993—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with chromium, molybdenum or tungsten
    • 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
    • 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
    • B01J27/0515—Molybdenum with iron group metals or platinum group metals
    • B01J35/19—
    • B01J35/40—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/038—Precipitation; Co-precipitation to form slurries or suspensions, e.g. a washcoat
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/04—Mixing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
    • B01J37/343—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of ultrasonic wave energy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/02—Preparation of oxygen
    • C01B13/0203—Preparation of oxygen from inorganic compounds
    • C01B13/0207—Water
    • 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
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/30—Treatment of water, waste water, or sewage by irradiation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/725—Treatment of water, waste water, or sewage by oxidation by catalytic oxidation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/08—Nanoparticles or nanotubes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/10—Photocatalysts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • 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

The present invention relates to nanocomposites comprising molybdenum disulfide (MoS2), nickel, and silver and their use for photocatalytic water splitting to produce hydrogen and oxygen from natural or purified water under irradiation with visible light. In addition, the invention also relates to a method for synthesizing said nanocomposites.

Description

NANOCOMPOSITES FOR PHOTOCATALYTIC WATER SPLITTING USING VISIBLE LIGHT AND METHOD FOR SYNTHESIS THEREOF
Field of invention
The present invention relates to nanocomposites comprising molybdenum disulfide (M0S2), nickel, and silver and their use for photocatalytic water splitting to produce hydrogen and oxygen from natural or purified water under irradiation with visible light. In addition, the invention also relates to a method for synthesizing said nanocomposites.
Background
Solar energy is the cleanest and most abundant energy source at mankind’s disposal. Emphasizing on solar energy usage is much more urgent today due to the depletion of fossil fuels, excessive CO2 emissions, and irreversible global warming consequences. Solar energy can be directly converted to electricity and heat, or indirectly to chemical energy stored in forms of organic and inorganic substances, which are feasible for transportation and flexible usages. Among these substances, hydrogen (H2) produced from water (H2O) splitting by using sunlight is one of the most promising products, which takes advantage of the abundance of water on earth. When H2 is burned, only clean steam (water) is produced. However, H2 cannot be produced effectively from water by irradiation with natural light. Efficient photocatalysts are needed to decompose water molecules into hydrogen and oxygen molecules in the photocatalytic hydrogen evolution.
Theoretically, only photons, water, and a photocatalyst are needed in photocatalytic hydrogen evolution (PHE). A good photocatalyst should be cheap to produce, have high catalytic efficiency, be stable over long-periods of time, reusable, and it should especially have the capability to decompose water by itself without additional additives. However, present photocatalysts are still far from commercial or industrial applicability and feasibility. For example, semiconducting CdS-based materials have been developed and reported in outstanding scientific journals. However, materials such as e.g., polyoxo-Ti/CdS/MIL, Cdots-C3N4, or Bi4NbOeCI require the use of sophisticated synthesis processes under rigorous laboratory conditions, and their hydrogen production efficiency is actually under expectation when considering the high-power light source employed in the reactions.
20185096 prh 02 -03- 2020
Semiconducting materials take a key role in current photocatalysts. The photoexcited electrons and holes of the semiconducting material are involved in the reduction and oxidation reaction of water, producing H2 and O2 consequently. To facilitate the redox reaction, cocatalysts are usually employed to form a Z-Scheme 5 photocatalyst in order to expand the photon absorption range. Effective separation of photoexcited electrons and holes is also crucial for water splitting, and a traditional solution is adding electrolytes as hole scavengers or electron donors, ensuring the reduction of the hydrogen radical (H ) to H2 by electrons. The necessity of cocatalysts and additional electrolytes increases the cost of evolved H2 and 10 makes the H2 evolution reaction too complicated to maintain for long periods.
Difficulties also exist in the selection of appropriate semiconducting matrix materials and matchable active sites for water reduction. For this reason, properly designed photocatalysts are still needed that are cheap and easy to prepare, can be used without additives, and have a wide light absorption range as well as good separation 15 ability of photogenerated electrons and holes.
It has been reported that photocatalytic nanocrystalline cobalt (II) oxide nanoparticles can be used to split water in photocatalytic hydrogen evolution. Said nanoparticles are synthesized from cobalt oxide micropowders using femtosecond laser ablation or mechanical ball milling.
Summary of the invention
It was surprisingly found that a heterojunctional MoS2-Ag-Ni complex can be used as a photocatalyst to produce hydrogen gas from water under irradiation with visible light. In addition, the inventors were able to produce such a complex.
The first aspect of the present invention is a nanocomposite. According to the 25 invention, said nanocomposite comprises layered molybdenum disulfide (M0S2), nickel, and silver; or consists of those. Said nanocomposite can be used for photocatalytic water-splitting to produce hydrogen and oxygen from purified or natural water under irradiation with visible light.
The second aspect of the present invention is a method for producing said 30 nanocomposites. According to the invention, said method comprises the steps of
a. mixing flakes of layered molybdenum disulfide and nickel nanopowder,
b. suspending the mixture of step a. in water,
c. adding an aqueous solution of a silver salt to the mixture of step b.,
d. sonicating the mixture of step c.,
e. recovering the formed photocatalytic nanocomposites.
The third aspect of the present invention is the use of the nanocomposites here described or produced as described here for the photocatalytic evolution of hydrogen from water.
The fourth aspect of the present invention is a method for producing hydrogen by photocatalytic water splitting. According to the invention, said method comprises the steps of contacting said the nanocomposites here described with water to form a suspension, irradiating said suspension of nanocomposites in water with light to evolve hydrogen-containing gas, and recovering the hydrogen-containing gas.
The fifth aspect of the present invention is the use of the nanocomposites here described or produced for water purification during water splitting.
Brief description of the figures
FIG. 1 is a graph showing the schematic diagram of photocatalyst promoted water splitting under visible light illumination.
FIG. 2 is a graph showing absorbance of the synthesized photocatalyst.
FIG. 3 is a graph showing different hydrogen production efficiency of nanocomposites with contents of molybdenum disulfide, nickel, and silver.
FIG. 4 is a graph showing the increase in hydrogen concentration due to hydrogen evolution during four reaction cycles of hydrogen evolution from pure water under visible light illumination.
FIG. 5 is a graph showing the increase in hydrogen concentration due to hydrogen evolution during long-term water splitting from pure and river water.
Detailed description
The target of the invention was to develop a novel photocatalyst and a facile route for the synthesis of said catalyst. The invention solves the problems of how to join M0S2 flakes and nickel nanoparticles together and provides a cheap but efficient photocatalyst for hydrogen production from water even without assistance of any extra cocatalyst or electrolyte.
As used herein, the term “nanocomposite” refers to a composite formed from a nickel nanoparticle and M0S2. The M0S2 may be in the form of flakes. Silver is used to adhere nickel nanoparticles to the M0S2.
As used herein, the term “nanoparticle” refers to a discrete particle with an average size from tens of nanometers to hundreds of nanometers.
As used herein, the expression “visible light” refers to electromagnetic radiation with a wavelength of between about 300 and about 750 nm.
As used herein, any percentages refer to weight percent of the total weight.
In the present application, any ratios given correspond to weight ratios of the individual components mentioned.
Figure 1 presents a schematic diagram showing the mechanism of the hydrogen evolution reaction promoted by the synthesized photocatalyst. Absorbed visible light photons excite electrons from the valence band of M0S2 to its conduction band, with holes in the valence band. Those electrons then migrate through the silver buffer layer to the surface of nickel. Such a process inhibits the recombination of electrons and holes. Therefore, more excited electrons are involved in the water reduction. Hydrogen and oxygen are then produced by the participation of electrons and holes.
The challenge of constructing an efficient photocatalyst lies first in the combination of suitable semiconducting materials and active metal particles. Commercial M0S2 multilayer flakes have an energy bandgap of 1.3 eV, which is suitable to excite electrons from valence band to conduction band by absorbed photons of visible light. The nickel nanopowder used in this invention is in the form of particles with an average diameter of approximately 200 nm. These nickel particles are active sites for accumulation of electrons, and thus facilitate the reduction of water to hydrogen. To attach nickel particles to M0S2 flakes with an average size of 1 pm, it is necessary to find a buffer component that will adhere to both of them, thereby sticking the two components together.
One embodiment of the invention is a method for producing said nanocomposites comprising the steps of mixing flakes of molybdenum disulfide and nickel nanoparticles, suspending the mixture in water, adding a solution of a silver compound, sonicating the mixture, and recovering and drying the formed nanocomposites.
The photocatalytic nanocomposites are synthesized by first weighing and mixing layered M0S2 flakes and nickel nanopowder with an average particle diameter of 200 nm in an Erlenmeyer flask. Addition of ultra-pure water and vigorous mixing or shaking provides a suspension in which the two powders are evenly distributed. A solution of silver compound is added, and the mixture is reacted in a heated water bath under sonication to fuse the components into the photocatalytic nanocomposites.
In one embodiment of the present invention, photocatalytic nanocomposites are constructed by joining nickel nanoparticles to layered M0S2 using silver nanoclusters as a buffer component.
Silver nitrate solution provides silver nanoclusters with an average diameter of 1 to 20 nm, which can locate to the defect sites of M0S2 and also adhere to the surface of nickel particles.
As used herein, the term “ultra-pure water” is defined as water that is purified with a Milli-Q Integral Water Purification System (or similar) under the condition of 18.2 ΜΩ cm @ 25 °C.
In one embodiment of the invention, the ultra-pure water used in the synthesis is replaced with distilled or deionized water, or water purified by any other method to lesser specifications. In another embodiment, the water is tap water.
As used herein, the term “tap water” is defined as water that is sufficiently purified to allow its household use for drinking, washing, cooking, and others.
In one embodiment of this invention, the silver compound is a salt of silver, preferably a soluble inorganic salt of silver, preferably fluoride, nitrate, or any mixture thereof, more preferably nitrate.
In one embodiment of the present invention the temperature of the water bath is 40 to 90 °C, preferably 50 to 80 °C, more preferably around 70 °C.
In one embodiment of this invention, the reaction time is 15 min to 10 hours, preferably 1 to 8 hours, more preferably 2 to 6 hours, still more preferably 3 to 5 hours, most preferably 4 hours. The term “reaction time” is defined as the length of time for which the reaction mixture is subjected to sonication.
In one embodiment of the present invention, the frequency of the ultrasound used is less than 100 kHz, preferably less than 70 kHz, more preferably less than 50 kHz, still more preferably 25 to 50 kHz, most preferably approximately 35 kHz.
As used herein, the term “layered molybdenum disulfide” refers to naturally occurring M0S2 flakes or synthesized M0S2 flakes consisting of at least 99 % M0S2. The flake size ranges from 200 nm χ 200 nm to 10 pm χ 10 pm, with layer thicknesses from 0.67 nm to 1 pm.
The nickel nanopowder used in the method of the present invention is in the form of nickel particles that have an average diameter of 200 nm and consist of > 99 % nickel.
In one embodiment of the present invention, the physical form of the M0S2 flakes may differ. The physical form of the M0S2 that can be used include, but are not limited to, flakes, grains, nanorods, shavings, discs, and others.
In one embodiment of the present invention, smaller M0S2 particles are utilized to increase the surface area of the nanocomposites.
In one embodiment of the present invention, the nanocomposite is immobilized on a surface or joined together to join a porous surface by any means known to a person skilled in the art. As a non-limiting example, the immobilization may be done with an adhesive.
In one embodiment of the present invention, the nanocomposites are recovered from the reaction mixture using any suitable method known to a person skilled in the art. Such methods include, but are not limited to, filtration, decanting, and centrifugation followed by removal of the supernatant.
The synthesized nanocomposites were analyzed by methods known to a person skilled in the art such as SEM, TEM, and XPS.
Figure 2 shows that photocatalytic nanocomposites according to the present invention have significant absorption of light in the entire visible light range (400 to 750 nm). Such absorption ability enables employment of all incident visible light photons.
In one embodiment of the invention, the photocatalytic nanocomposites consist of layered molybdenum disulfide, silver, and nickel.
20185096 prh 02 -03- 2020
In one embodiment of the invention, the photocatalytic nanocomposite comprises nickel and silver in a ratio of 10:1 to 1:10, preferably 5:1 to 1:5, more preferably 3:1 to 1:3, in particularly 2:5 to 4:5. In one embodiment the nanocomposites comprise 84 % M0S2, 10 % silver, and 6 % nickel.
In one embodiment of the present invention, the photocatalytic nanocomposites are synthesized by one or several repetitions of the synthesis steps in order to increase the amount of successfully synthesized nanocomposites. In one embodiment the synthesis is completed in one treatment cycle.
In one embodiment of the present invention, the synthesized photocatalytic nanocomposites are recovered, dried and stored dry in powder form. The nanocomposites may be recovered and dried by any suitable methods known to a person skilled in the art. These methods include, but are not limited to, filtering and air drying the nanocomposites.
In one embodiment of the present invention the nanocomposites are used for the photocatalytic evolution of hydrogen from water.
In one embodiment of the present invention, the nanocomposites are used for water purification. Organic matter in natural water may be decolorized simultaneously while nanocomposites in water to be purified are exposed to light as during water splitting. The total organic carbon (TOC) measurement of lake water shows that the TOC level drops from 14.1 ppm to 9.65 ppm, and the original brownish color is totally removed, and water cleared. The composites have 5 mg weight, and the whole system was under white light LED irradiation for 10 hours.
In one embodiment of the present invention, the nanocomposites are used for treatment of liquid comprising water and organic substances.
In one embodiment of the present invention, the method for producing hydrogen by photocatalytic water splitting comprises the steps of contacting the nanocomposites with water, irradiating the suspension of nanocomposites in water with light, and recovering the hydrogen-containing gas.
To investigate the optimal contents of M0S2, nickel and silver, samples with different compositions may be synthesized using the above method and tested in identical conditions as the example above. All reactions may be performed at room temperature under atmospheric pressure. The light source may be LED lamps with average power of 0.2 W. Cut-off Filters ensure the wavelength of the incident light
20185096 prh 02 -03- 2020 may be larger than 350 nm. Incident light may be perpendicularly illuminated onto the bottom of a quartz bottle, which contains the reaction system including distilled water and synthesized photocatalyst. The pH of the water may vary from 5.0 to 8.5.
Figure 3 shows the hydrogen production efficiency of various catalysts. Commercial
M0S2 has a very weak photocatalytic ability for hydrogen evolution, only 0.6 pmolg1W1It1. The binary catalysts tested were M0S2-N1, MoS2-Ag and Ag-Ni. All of the three binary catalysts have increased hydrogen production efficiency compared with commercial M0S2. With silver employed as a buffering component, MoS2-Ag-Ni ternary complexes have greatly improved photocatalytic ability. E.g. a photocatalytic 10 nanocomposite consisting of 84% M0S2, 10% Ag and 6% Ni has a hydrogen production rate of 68 pmolg’1W’1lT1.
The hydrogen production rate may be determined by using the following equipment: a) a sealable transparent quartz-glass flask for sample reaction with known dimensions and volume, b) a device equipped with light emitting diode (LED) as light 15 source with a known and measured irradiation power of 0.495 W and a magnetic stirring mechanism, c) a timer, d) a syringe for sampling gas, and e) a gas chromatograph to measure amount of hydrogen in the gas samples.
Step 1: Calibrate the gas chromatograph (GC) with gas samples of different H2 concentration. Gas samples refer to H2 mixed with Ar carrier gas in room 20 temperature (25 °C).
Step 2: The sample flasks were filled with 42 mL of gas volume and 20 mL of waternanocomposite mixture.
Step 3: The flasks were stirred and irradiated by white LED light from the bottom of the flask for a known period of time.
Step 4: A sample of gas from the reaction flask was obtained for H2 content analysis. The H2 concentration values in the gas samples from reaction flasks were measured by using the gas chromatograph.
In one embodiment of the present invention, the water splitting, or the water purification is performed by subjecting the photocatalytic nanocomposites to 30 irradiation with artificial light or natural ambient light.
In one embodiment of the present invention, the water splitting is performed by subjecting the photocatalytic nanocomposites to irradiation with sunlight.
20185096 prh 02 -03- 2020
As used herein, the term “sunlight” refers to electromagnetic radiation corresponding to the irradiance spectrum of the sun with wavelengths from 250 to 2500 nm.
In one embodiment of the present invention, the water splitting is performed by subjecting the photocatalytic nanocomposites to irradiation with light with 5 wavelengths from 250 to 2500 nm, preferably from 250 to 750 nm, more preferably from 350 to 700 nm.
In one embodiment of the invention, the efficiency of the water splitting may be further improved by bringing the photocatalytic nanocomposites into contact with an additional cocatalyst or another additive.
Figure 4 shows the cumulative hydrogen evolution during several consecutive reaction cycles. One reaction cycle lasted for 10 hours, without water circulation. An average hydrogen production rate was around 75 pmol g’1W’1lT1. After repeating for 4 cycles, the catalyst was stored in the same bottle (without inert gas protection) for 3 months in the dark. Then the same reaction cycle was repeated two times.
There was no significant decrease of hydrogen production efficiency over the course of the experiment.
The photocatalyst was also active in the case of natural water. Figure 5 shows cumulative long-term hydrogen evolution for photocatalytic splitting of distilled water (pH: 6.0 to 7.5) and river water (pH: 5.5 to 6.2). Reaction conditions were as 20 mentioned above. During the continuous 10-day reactions, the water was not changed. In the case of distilled water, the average hydrogen production rate was around 45 pmol g’1W’1lT1, up to 60% of efficiency of short-term (10 hours) water splitting tests. River water was taken from Oulujoki River (Tuira, Oulu, Finland). The hydrogen production efficiency from river water was lower than from distilled water, 25 but it still showed an average production rate of 34 pmol g^ W^h’1. Therefore, the synthesized photocatalyst provides potential application condition of natural water, which is beneficial to large-scale production.
As used herein, the term “natural water” refers to any water taken from a natural source that is not purified or treated in any way after collecting.
In one embodiment of the present invention, the source for natural water can be any body of water found in nature such a stream, river, spring, well, lake, sea, ocean, reservoir, or similar.
20185096 prh 02 -03- 2020
In one embodiment of the present invention, hydrogen may be generated from purified water or natural water, or any mixture thereof. In another embodiment of the invention, hydrogen can be produced from fresh water or from salt water, or any mixture thereof.
In one embodiment of the invention, the hydrogen-containing gas produced by water splitting is collected and the component gases separated by any method known to a person skilled in the art. In another embodiment of the present invention the separated hydrogen gas is further compressed and stored for later use. In yet another embodiment of the invention, the oxygen produced in the water cleavage is 10 also collected, separated, and stored for later use.
The cost of the synthesized photocatalyst in this invention is estimated by the summation of materials and electricity costs during the entire synthesis process. The total cost is around 1 euro per gram photocatalyst assuming the use of commercially sourced raw materials acquired at market price and typical end-user 15 cost for electricity in Finland (approximately 4 to 5 c/kWh).
The invention is described below with the help of examples. The examples are given only for illustrative purpose and they do not limit the scope of the invention.
Examples
General procedure for evolution of hydrogen by the synthesized photocatalyst: 10 20 mg of the synthesized photocatalytic nanocomposites were dispersed in 20 mL of distilled water in a quartz bottle. The bottle was irradiated with a LED lamp (0.2 W), with the incident light perpendicular to the bottom of the bottle. A cutoff filter was used to ensure that the wavelength of the irradiation was over 350 nm. Magnetic stirring was employed to help collect the produced hydrogen. The reaction was 25 carried out in ambient pressure, at room temperature without the addition of a protective or inert atmosphere in the flask.
Example 1: Synthesis of photocatalyst
For synthesizing 10 mg of nanocomposite of(MoS2)84AgioNie, M0S2 (8.4 mg) and nickel nanopowder (0.6 mg) were weighed and placed in a 125 ml Erlenmeyer flask 30 with 0.926 mL of AgNOs solution (0.01 mol/L). Approximately half the maximum volume of the flask of ultra-pure water was added and the mixture shaken vigorously to produce an evenly distributed suspension. Freshly prepared silver nitrate solution was added, and the flask sealed and placed in a heated water bath (70 °C) and sonicated for 4 hours at 35 kHz. The synthesized ternary photocatalyst comprised 2 to 10 wt. % nickel, 1 to 15 wt. % silver and the balance M0S2. After synthesis, the flask was kept in the water bath (switched off) and allowed to cool down to room temperature. The photocatalytic nanocomposites were recovered by filtration.
The nanocomposites were confirmed by microscopic and spectroscopic determinations.
Example 2: Hydrogen evolution using photocatalyst
The photocatalytic nanocomposites were used to produce hydrogen gas according to the general procedure detailed above.
The amount of produced hydrogen was determined and calculated as follows. The concentration of produced hydrogen was measured by gas chromatography. Based on the measured concentration and the known total gas volume the amount of hydrogen gas produced was calculated. For determining the efficiency of the catalyst, the amount of catalyst in grams and applied power in watts were also taken into account by normalizing (dividing) the result with the grams and watts. Since the irradiation time was also known, the hourly hydrogen production rate was obtained by dividing the result by the irradiation time in hours.
The catalyst Cdots-Csisk is reported with an optimal production rate of approximately 45 pmol/h, however, it can be calculated to be only 1.9 pmol/(h g W) when the catalyst amount (80 mg) and lamp power (300 W) are considered.
Example 3: Comparative examples
The ratio of nickel and silver in the nanocomposite is relevant to the photocatalytic ability of the synthesized catalyst. To compare hydrogen production rates of various compositions, groups of binary and ternary catalysts were synthesized. All reactions were performed in accordance with the procedure detailed in Example 2 for production of hydrogen and measuring the amount of hydrogen produced. The pH of the water varied from 5.0 to 8.5. Commercial M0S2 showed a very weak photocatalytic ability for hydrogen evolution, only 0.6 pmol g'1W'1lT1. Binary catalysts included were M0S2-N1, MoS2-Ag and Ag-Ni. All of the three binary catalysts showed increased hydrogen production efficiency compared with commercial M0S2. With silver employed as a buffering component, MoS2-Ag-Ni ternary complexes showed greatly improved photocatalytic ability. An exemplary
20185096 prh 02 -03- 2020 composition consisting of 84% M0S2, 10% Ag and 6% Ni (a 5:3 ratio of nickel to silver) had a hydrogen production rate of 68 pmol g^ W h’1.
Example 4: Time course/life cycle of photocatalyst
Hydrogen evolution reaction cycles were performed according to the general 5 procedures. One cycle lasted for 10 hours, without water circulation. An average hydrogen production rate for the first cycle was around 75 pmolg’1W’1lT1. After repeating for 4 cycles, the catalyst was stored in the same bottle (without inert gas protection) for 3 months. After storage, the same reaction cycle was repeated two times. No significant decrease in hydrogen production efficiency was seen.
Example 5: Hydrogen evolution under irradiation with natural sunlight
The photocatalytic nanocomposites produced in Example 1 were placed in a flask in distilled water and irradiated by natural sunlight indoors. The produced hydrogen was measured once a day with a portable H2 detector (0 to 1000 ppm). Measurements were taken in Oulu (65°01'N 25°28'E) from 27th September 2016 to 15 3rd October 2016. The weather during this period was mainly cloudy or overcast in the daytime. The measured concentration of H2 was 39 ppm against a 50 ml volume.
For comparison, the atmosphere contains approximately 0.5 ppm hydrogen. To estimate the efficiency of the synthesized catalyst, the annual average total solar radiation for 60° N district was used (179050 cal/cm2). It is equivalent to an average 20 radiation power of 237.6 W/m2 The bottom of the flask was approximately 28 cm2, thus the actual solar light radiation power in the experiment is around 0.66 W. Therefore, the average H2 production efficiency is estimated to be 0.35 pmol g-1 h-1 W-1 and the highest value, measure on 29 September, is 0.97 pmol g-1 It1 W1.
Example 6: Water purification
The nanocomposites of example 1 were also used for water purification during water splitting. By adding 5 mg of the nanocomposite to 50 ml of natural lake water a significant decoloration was seen after irradiation with visible-light LEDs for 10 h. During the experiment, the natural brownish color of the water was completely 30 removed as the total organic carbon (TOC) measured from the sample dropped from
14.1 ppm to 9.65 ppm. After the irradiation the water was completely clear and colorless.

Claims (13)

PatenttivaatimuksetThe claims 1. Nanokomposiitti, jolloin mainittu nanokomposiitti sisältää tai koostuu seuraavista:A nanocomposite, wherein said nanocomposite comprises or consists of: a. kerrostettu molybdeenidisulfidi (M0S2),a. layered molybdenum disulphide (M0S2), b. nikkeli jab. Nickel and c. hopea, tunnettu siitä, että mainitussa nanokomposiitissa hopea yhdistää kerrostetun molybdeenidisulfidin ja nikkelin.c. silver, characterized in that in said nanocomposite, silver combines layered molybdenum disulfide and nickel. 2. Patenttivaatimuksen 1 mukainen nanokomposiitti, tunnettu siitä, että mainittu nanokomposiitti sisältää ainakin 98 paino-%Nanocomposite according to claim 1, characterized in that said nanocomposite contains at least 98% by weight a. kerrostettua molybdeenidisulfidia,a. layered molybdenum disulphide, b. nikkeliä jab. Nickel and c. hopeaa, jolloin loppuosa on epäpuhtauksia, kuten hopean ja nikkelin oksideja.c. silver, with the remainder being impurities such as oxides of silver and nickel. 3. Patenttivaatimuksen 1 tai 2 mukainen nanokomposiitti, tunnettu siitä, että mainittu nanokomposiitti sisältää nikkeliä ja hopeaa suhteessa 10:1 - 1:10, edullisesti 5:1-1:5, edullisemmin 3:2 - 1:3 ja edullisimmin 2:5 - 4:5.Nanocomposite according to claim 1 or 2, characterized in that said nanocomposite contains nickel and silver in a ratio of 10: 1 to 1:10, preferably 5: 1 to 1: 5, more preferably 3: 2 to 1: 3 and most preferably 2: 5 - 4: 5. 4. Jonkin edellä olevista patenttivaatimuksista mukainen nanokomposiitti, tunnettu siitä, että mainittu nanokomposiitti sisältää painoprosentteina,Nanocomposite according to any one of the preceding claims, characterized in that said nanocomposite contains, by weight, a. 2- 25 % nikkeliä jaa. 2-25% nickel and b. 1-15 % hopeaa, jolloin loppuosa on kerrostettua molybdeenidisulfidia, joka sisältää alle 1 %:n verran epäpuhtausjäämiä.b. 1-15% silver, the remainder being layered molybdenum disulphide containing less than 1% impurity residues. 5. Patenttivaatimuksen 4 mukainen nanokomposiitti, tunnettu siitä, että mainittu nanokomposiitti sisältää painoprosentteina:Nanocomposite according to claim 4, characterized in that said nanocomposite contains in weight percent: a. 83 % kerrostettua molybdeenidisulfidia,a. 83% layered molybdenum disulphide, b. 10 % nikkeliä jab. 10% nickel and c. 6 % hopeaa, jolloin loppuosa on epäpuhtauksia, kuten hopean ja nikkelin oksideja.c. 6% silver, with the remainder being impurities such as oxides of silver and nickel. 6. Jonkin edellä olevista patenttivaatimuksista mukainen nanokomposiitti, tunnettu siitä, että mainittu nanokomposiitti ei sisällä lisäelektrolyyttejä, pelkistimiä (sacrificial electron donor), hapettuvia aineita (hole scavenger) tai muita uhrautuvia reagensseja (sacrificial reagent).Nanocomposite according to any one of the preceding claims, characterized in that said nanocomposite does not contain additional electrolytes, reducing agents (sacrificial Electron donor), oxidizing agents (hole scavenger) or other sacrificial reagents. 7. Menetelmä jonkin patenttivaatimuksista 1-6 mukaisten nanokomposiittien tuottamiseksi sisältäen seuraavat vaiheet:A method for producing nanocomposites according to any one of claims 1 to 6, comprising the steps of: a. kerrostetun molybdeenidisulfidin hiutaleiden ja nikkelinanojauheen sekoittaminena. mixing the layered molybdenum disulfide flakes and nickel nanopowder b. vaiheen a. seoksen liettäminen veteen,b. slurrying the mixture of step a. in water, c. vesipitoisen hopeasuolaliuoksen lisääminen vaiheen b. suspension,c. adding an aqueous silver salt solution to the suspension of step b. d. vaiheen c. suspension sonikaatio,d. step c. suspension sonication, e. muodostettujen fotokatalyyttisten nanokomposiittien ottaminen talteen.e. recovering the formed photocatalytic nanocomposites. 8. Patenttivaatimuksen 7 mukainen menetelmä, jossa menetelmä sisältää edelleen vaiheen, jossa vaiheen c. suspensio lämmitetään vesihauteessa vaiheidenThe method of claim 7, wherein the method further comprises the step of step c. the suspension is heated in a water bath in steps c. ja d. välissä.c. and d. between. 9. Patenttivaatimuksen 7 tai 8 mukainen menetelmä, jossa menetelmä sisältää edelleen vaiheen, jossa vaiheesta d. saatu seos jäähdytetään tai sen annetaan jäähtyä ympäristön lämpötilaan vaiheiden d. ja e. välillä.The method of claim 7 or 8, wherein the method further comprises the step of step d. the resulting mixture is cooled or allowed to cool to ambient temperature in steps d. and e. 10. Jonkin patenttivaatimuksista 1-6 mukaisen tai patenttivaatimusten 7-9 mukaisella menetelmällä tuotetun nanokomposiitin käyttö vedyn kehittämiseksi fotokatalyyttisesti vedestä tai veden puhdistamiseen.Use of a nanocomposite according to any one of claims 1 to 6 or produced by the process according to claims 7 to 9 for photocatalytically generating hydrogen or for purifying water. 11. Menetelmä vedyn tuottamiseksi fotokatalyyttisen vedenerotuksen avulla, johon sisältyvät seuraavat vaiheet:11. A method for producing hydrogen by photocatalytic water separation, comprising the steps of: ajonkin patenttivaatimuksista 1-6 mukaisen nanokomposiittien saattaminen kosketuksiin veden kanssa suspension muodostamiseksicontacting the nanocomposites according to any one of claims 1 to 6 with water to form a suspension b. nanokomposiittisuspension säteilyttäminen vedessä valon avulla jab. irradiating the nanocomposite suspension in water with light; and c. vetyä sisältävän kaasun ottaminen talteen.c. recovery of hydrogen-containing gas. 12. Patenttivaatimuksen 11 mukainen menetelmä vedyn tuottamiseksi, tunnettu siitä, että tuotettu vety erotetaan, kerätään talteen ja varastoidaan tulevaa käyttöä varten.A method for producing hydrogen according to claim 11, characterized in that the produced hydrogen is separated, collected and stored for future use. 13. Menetelmä veden puhdistamiseksi, joka sisältää jonkin patenttivaatimuksista 1-6 mukaisen tai jonkin patenttivaatimuksista 7-9 mukaisella menetelmällä tuotetun nanokomposiitin saattamisen kosketuksiin puhdistettavan veden kanssa.A method of purifying water comprising contacting a nanocomposite according to any one of claims 1 to 6 or produced by a method according to any one of claims 7 to 9 with water to be purified.
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