WO2019150000A1 - 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

Info

Publication number
WO2019150000A1
WO2019150000A1 PCT/FI2019/050069 FI2019050069W WO2019150000A1 WO 2019150000 A1 WO2019150000 A1 WO 2019150000A1 FI 2019050069 W FI2019050069 W FI 2019050069W WO 2019150000 A1 WO2019150000 A1 WO 2019150000A1
Authority
WO
WIPO (PCT)
Prior art keywords
water
nanocomposite
nanocomposites
nickel
silver
Prior art date
Application number
PCT/FI2019/050069
Other languages
French (fr)
Inventor
Xinying SHI
Wei Cao
Marko HUTTULA
Original Assignee
Wmz - Nanosurfaces Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Wmz - Nanosurfaces Oy filed Critical Wmz - Nanosurfaces Oy
Publication of WO2019150000A1 publication Critical patent/WO2019150000A1/en

Links

Classifications

    • 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
    • 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
    • B01J23/76—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

Definitions

  • 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.
  • the invention also relates to a method for synthesizing said nanocomposites.
  • Solar energy is the cleanest and most abundant energy source at civilization’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.
  • 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.
  • H2 When H2 is burned, only clean steam (water) is produced.
  • 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.
  • 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.
  • 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.
  • materials such as e.g., polyoxo-Ti/CdS/MIL, Cdots-C3N 4 , or BUNbOsCI 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.
  • 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 Fh and O 2 consequently.
  • cocatalysts are usually employed to form a Z-Scheme photocatalyst in order to expand the photon absorption range.
  • 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.
  • a heterojunctional MoS 2 -Ag-Ni complex can be used as a photocatalyst to produce hydrogen gas from water under irradiation with visible light.
  • the inventors were able to produce such a complex.
  • the first aspect of the present invention is a nanocomposite.
  • said nanocomposite comprises layered molybdenum disulfide (M0S 2 ), 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 nanocomposites.
  • 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,
  • step 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • nanoparticle refers to a discrete particle with an average size from tens of nanometers to hundreds of nanometers.
  • visible light refers to electromagnetic radiation with a wavelength of between about 300 and about 750 nm.
  • any percentages refer to weight percent of the total weight.
  • 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.
  • 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.
  • 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 MW cm @ 25 °C.
  • 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.
  • the water is tap water.
  • tap water is defined as water that is sufficiently purified to allow its household use for drinking, washing, cooking, and others.
  • 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.
  • the temperature of the water bath is 40 to 90 °C, preferably 50 to 80 °C, more preferably around 70 °C.
  • 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.
  • reaction time is defined as the length of time for which the reaction mixture is subjected to sonication.
  • 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.
  • 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 c 200 nm to 10 pm c 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.
  • 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.
  • smaller M0S2 particles are utilized to increase the surface area of the nanocomposites.
  • 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.
  • the immobilization may be done with an adhesive.
  • 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.
  • the photocatalytic nanocomposites consist of layered molybdenum disulfide, silver, and nickel.
  • 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.
  • the nanocomposites comprise 84 % M0S2, 10 % silver, and 6 % nickel.
  • 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.
  • 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.
  • the nanocomposites are used for the photocatalytic evolution of hydrogen from water.
  • 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.
  • the nanocomposites are used for treatment of liquid comprising water and organic substances.
  • 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.
  • 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 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 pmol-g 1 -W 1 -h 1 .
  • 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.
  • silver employed as a buffering component MoS2-Ag-Ni ternary complexes have greatly improved photocatalytic ability.
  • a photocatalytic nanocomposite consisting of 84% M0S2, 10% Ag and 6% Ni has a hydrogen production rate of 68 pmol -g 1 -W 1 -h ⁇ 1 .
  • 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 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.
  • LED light emitting diode
  • 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 temperature (25 °C).
  • Step 2 The sample flasks were filled with 42 mL of gas volume and 20 mL of water- nanocomposite 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.
  • the water splitting, or the water purification is performed by subjecting the photocatalytic nanocomposites to irradiation with artificial light or natural ambient light.
  • the water splitting is performed by subjecting the photocatalytic nanocomposites to irradiation with sunlight.
  • the term“sunlight” refers to electromagnetic radiation corresponding to the irradiance spectrum of the sun with wavelengths from 250 to 2500 nm.
  • the water splitting is performed by subjecting the photocatalytic nanocomposites to irradiation with light with wavelengths from 250 to 2500 nm, preferably from 250 to 750 nm, more preferably from 350 to 700 nm.
  • 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 1 -W 1 -lT 1 .
  • 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.
  • FIG. 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 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 1 -W 1 -lT 1 , up to 60% of efficiency of short-term (10 hours) water splitting tests. River water was taken from Ouvieroki River (Tuira, Oulu, Finland).
  • the hydrogen production efficiency from river water was lower than from distilled water, but it still showed an average production rate of 34 pmol-g 1 -W 1 -lT 1 . Therefore, the synthesized photocatalyst provides potential application condition of natural water, which is beneficial to large-scale production.
  • natural water refers to any water taken from a natural source that is not purified or treated in any way after collecting.
  • 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.
  • hydrogen may be generated from purified water or natural water, or any mixture thereof.
  • hydrogen can be produced from fresh water or from salt water, or any mixture thereof.
  • 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.
  • the separated hydrogen gas is further compressed and stored for later use.
  • the oxygen produced in the water cleavage is 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 cost for electricity in Finland (approximately 4 to 5 c/kWh).
  • nanocomposites were confirmed by microscopic and spectroscopic determinations.
  • 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.
  • 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-C3N 4 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.
  • the ratio of nickel and silver in the nanocomposite is relevant to the photocatalytic ability of the synthesized catalyst.
  • 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 1 -W 1 -h ⁇ 1 .
  • 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.
  • MoS2-Ag-Ni ternary complexes showed greatly improved photocatalytic ability.
  • Hydrogen evolution reaction cycles were performed according to the general procedures. One cycle lasted for 10 hours, without water circulation. An average hydrogen production rate for the first cycle was around 75 mhhoI ⁇ 1 L/ 1 ⁇ It 1 . 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 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.
  • the annual average total solar radiation for 60° N district was used (179050 cal/cm 2 ).
  • 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 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.
  • TOC total organic carbon

Abstract

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. The nanocomposites are characterized in that in said nanocomposites silver joins together the layered molybdenum disulfide and nickel nanoparticles. The method for synthesizing the nanocomposites comprises the step of sonicating a dispersion containg layered molybdenum disulfide flakes and nickel nanopowder suspended in water and a silver salt in solution in the dispersing medium.

Description

NANOCOMPOSITES FOR PHOTO CATALYTIC 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 BUNbOsCI 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. 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 Fh and O2 consequently. To facilitate the redox reaction, cocatalysts are usually employed to form a Z-Scheme 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 makes the hte 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 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 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 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 MW 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 c 200 nm to 10 pm c 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. 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 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 pmol-g 1 -W 1 -h 1. 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 nanocomposite consisting of 84% M0S2, 10% Ag and 6% Ni has a hydrogen production rate of 68 pmol -g 1 -W 1 -h·1.
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 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 temperature (25 °C).
Step 2: The sample flasks were filled with 42 mL of gas volume and 20 mL of water- nanocomposite 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 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. 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 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 1 -W 1 -lT1. 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 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 1 -W 1 -lT1, 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, but it still showed an average production rate of 34 pmol-g 1 -W 1 -lT1. 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. 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 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 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 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 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)84AgioNi6, M0S2 (8.4 mg) and nickel nanopowder (0.6 mg) were weighed and placed in a 125 ml Erlenmeyer flask 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-C3N4 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 1 -W 1 -h·1. 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 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 procedures. One cycle lasted for 10 hours, without water circulation. An average hydrogen production rate for the first cycle was around 75 mhhoI ^ 1 L/ 1 ·It1. 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 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 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 IT1 W-1 and the highest value, measure on 29 September, is 0.97 pmol g_1 IT1 w-1 .
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 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

Claims
1.A nanocomposite wherein said nanocomposite comprises, or consists of, a. layered molybdenum disulfide (M0S2),
b. nickel, and
c. silver,
characterized in that in said nanocomposite silver joins together the layered molybdenum disulfide and nickel.
2. The nanocomposite of claim 1 , characterized in that said nanocomposite comprises at least 98 % by weight of
a. layered molybdenum disulfide,
b. nickel, and
c. silver,
the balance being impurities such as oxides of silver or nickel.
3. The nanocomposite of claim 1 or 2, characterized in that said 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 and most preferably 2:5 to 4:5.
4. The nanocomposite of any of the preceding claims, characterized in that said nanocomposite comprises, by weight,
a. 2 to 25 % nickel, and
b. 1 to 15 % silver,
the balance being layered molybdenum disulfide including trace impurities in an amount that is less than 1 %.
5. The nanocomposite of claim 4, characterized in that said nanocomposite comprises, by weight,
a. 83 % layered molybdenum disulfide,
b. 10 % nickel, and
c. 6 % silver,
the balance being impurities such as oxides of silver or nickel.
6. The nanocomposite of any of the preceding claims, characterized in that said nanocomposite does not comprise additive electrolytes, sacrificial electron donors, hole scavengers, or other sacrificial reagents.
7. A method for producing the nanocomposites of any of claims 1 to 6 comprising 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 suspension of step b., d. sonicating the suspension of step c.,
e. recovering the formed photocatalytic nanocomposites.
8. The method of claim 7 wherein the method comprises a further step of warming the suspension of step c. in a water bath between steps c. and d.
9. The method of claims 7 or 8 wherein the method comprises a further step of cooling the mixture obtained from step d. or allowing it to cool to ambient temperature between steps d. and e.
10. Use of the nanocomposite of any of claims 1 to 6 or produced according to the method of claims 7 to 9 for the photocatalytic evolution of hydrogen from water or water purification.
11.A method for producing hydrogen by photocatalytic water splitting comprising the steps of
a. contacting the nanocomposites of any of claims 1 to 6 with water to form a suspension,
b. irradiating the suspension of nanocomposites in water with light, and c. recovering the hydrogen-containing gas.
12. The method for producing hydrogen of claim 1 1 , characterized in that the produced hydrogen is separated, collected and stored for future use.
13. The method for purifying water comprising contacting a nanocomposite of any of claims 1 to 6 or produced according to the method of claims 7 to 9 with water to be purified.
PCT/FI2019/050069 2018-02-02 2019-01-31 Nanocomposites for photocatalytic water splitting using visible light and method for synthesis thereof WO2019150000A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20185096 2018-02-02
FI20185096A FI128375B (en) 2018-02-02 2018-02-02 Nanocomposites for photocatalytic water splitting using visible light and method for synthesis thereof

Publications (1)

Publication Number Publication Date
WO2019150000A1 true WO2019150000A1 (en) 2019-08-08

Family

ID=65576378

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI2019/050069 WO2019150000A1 (en) 2018-02-02 2019-01-31 Nanocomposites for photocatalytic water splitting using visible light and method for synthesis thereof

Country Status (2)

Country Link
FI (1) FI128375B (en)
WO (1) WO2019150000A1 (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110583691A (en) * 2019-09-19 2019-12-20 南京工业大学 Reductive graphene oxide-molybdenum disulfide-silver ternary composite antibacterial material and preparation method and application thereof
CN110947405A (en) * 2019-11-08 2020-04-03 武汉科技大学 Regularly arranged g-C3N4Nanotube catalyst and method for preparing the same
CN111389469A (en) * 2020-05-15 2020-07-10 福州大学 Preparation method of photocatalytic heterojunction nano composite material for removing algae in water body
CN112536045A (en) * 2020-12-09 2021-03-23 华南师范大学 Silver/rhenium disulfide binary composite nano photocatalytic sterilization material and preparation method and application thereof
CN114772643A (en) * 2022-04-27 2022-07-22 广东省科学院生物与医学工程研究所 Composite nano material and preparation method and application thereof
CN114950491A (en) * 2022-03-09 2022-08-30 哈尔滨理工大学 Preparation of nickel-molybdenum-cadmium trimetal nano material constructed by polyacid and photocatalytic application of nickel-molybdenum-cadmium trimetal nano material
WO2023201298A3 (en) * 2022-04-13 2023-11-16 Drexel University Catalytic production of hydrogen from water

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103990472A (en) * 2014-06-09 2014-08-20 中国科学技术大学 Stable and efficient hydrogen production co-catalyst and preparation method thereof
CN107552073A (en) * 2017-09-13 2018-01-09 重庆大学 A kind of MoS2Preparation method of AIZS nano composite materials and products thereof and application

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103990472A (en) * 2014-06-09 2014-08-20 中国科学技术大学 Stable and efficient hydrogen production co-catalyst and preparation method thereof
CN107552073A (en) * 2017-09-13 2018-01-09 重庆大学 A kind of MoS2Preparation method of AIZS nano composite materials and products thereof and application

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
XINYING SHI ET AL: "Metallic Contact between MoS 2 and Ni via Au Nanoglue", SMALL, vol. 14, no. 22, 1 May 2018 (2018-05-01), DE, pages 1704526, XP055577340, ISSN: 1613-6810, DOI: 10.1002/smll.201704526 *
XU JIXIANG ET AL: "Noble metal-free NiCo nanoparticles supported on montmorillonite/MoS2heterostructure as an efficient UV-visible light-driven photocatalyst for hydrogen evolution", INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, ELSEVIER SCIENCE PUBLISHERS B.V., BARKING, GB, vol. 43, no. 3, 14 December 2017 (2017-12-14), pages 1375 - 1385, XP085331103, ISSN: 0360-3199, DOI: 10.1016/J.IJHYDENE.2017.11.129 *

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110583691A (en) * 2019-09-19 2019-12-20 南京工业大学 Reductive graphene oxide-molybdenum disulfide-silver ternary composite antibacterial material and preparation method and application thereof
CN110947405A (en) * 2019-11-08 2020-04-03 武汉科技大学 Regularly arranged g-C3N4Nanotube catalyst and method for preparing the same
CN110947405B (en) * 2019-11-08 2023-07-28 武汉科技大学 g-C in regular arrangement 3 N 4 Nanotube catalyst and method for preparing same
CN111389469A (en) * 2020-05-15 2020-07-10 福州大学 Preparation method of photocatalytic heterojunction nano composite material for removing algae in water body
CN112536045A (en) * 2020-12-09 2021-03-23 华南师范大学 Silver/rhenium disulfide binary composite nano photocatalytic sterilization material and preparation method and application thereof
CN114950491A (en) * 2022-03-09 2022-08-30 哈尔滨理工大学 Preparation of nickel-molybdenum-cadmium trimetal nano material constructed by polyacid and photocatalytic application of nickel-molybdenum-cadmium trimetal nano material
WO2023201298A3 (en) * 2022-04-13 2023-11-16 Drexel University Catalytic production of hydrogen from water
CN114772643A (en) * 2022-04-27 2022-07-22 广东省科学院生物与医学工程研究所 Composite nano material and preparation method and application thereof
CN114772643B (en) * 2022-04-27 2024-03-29 广东省科学院生物与医学工程研究所 Composite nano material and preparation method and application thereof

Also Published As

Publication number Publication date
FI20185096A1 (en) 2019-08-03
FI128375B (en) 2020-04-15

Similar Documents

Publication Publication Date Title
FI128375B (en) Nanocomposites for photocatalytic water splitting using visible light and method for synthesis thereof
Yi et al. The facile fabrication of 2D/3D Z-scheme g-C3N4/UiO-66 heterojunction with enhanced photocatalytic Cr (VI) reduction performance under white light
Mushtaq et al. 3D interconnected porous Mo-doped WO3@ CdS hierarchical hollow heterostructures for efficient photoelectrochemical nitrogen reduction to ammonia
US20220042184A1 (en) Preparation Method and Application of Non-noble Metal Single Atom Catalyst
Zhu et al. Fabrication of magnetically recoverable photocatalysts using g-C3N4 for effective separation of charge carriers through like-Z-scheme mechanism with Fe3O4 mediator
Liu et al. ZnIn2S4 flowerlike microspheres embedded with carbon quantum dots for efficient photocatalytic reduction of Cr (VI)
Hao et al. Zn‐Vacancy Engineered S‐Scheme ZnCdS/ZnS Photocatalyst for Highly Efficient Photocatalytic H2 Evolution
Shi et al. Synergetic effect of carbon dots as co-catalyst for enhanced photocatalytic performance of methyl orange on ZnIn2S4 microspheres
Omar et al. Microwave synthesis of zinc oxide/reduced graphene oxide hybrid for adsorption-photocatalysis application
Wang et al. Fabrication of noble-metal-free CdS nanorods-carbon layer-cobalt phosphide multiple heterojunctions for efficient and robust photocatalyst hydrogen evolution under visible light irradiation
Liu et al. Fabricated 2D/2D CdIn2S4/N-rGO muti-heterostructure photocatalyst for enhanced photocatalytic activity
Huang et al. Self-assembled MoS2-GO framework as an efficient cocatalyst of CuInZnS for visible-light driven hydrogen evolution
Danish et al. Novel ZnSQDs-SnO2/g-C3N4 nanocomposite with enhanced photocatalytic performance for the degradation of different organic pollutants in aqueous suspension under visible light
Chen et al. Efficient treament of organic pollutants over CdS/graphene composites photocatalysts
Yadav et al. Synthesis and photocatalytic Applications of functionalized carbon quantum dots
Cheng et al. Insights into charge transfer and solar light photocatalytic activity induced by the synergistic effect of defect state and plasmon in Au nanoparticle-decorated hierarchical 3D porous ZnO microspheres
Mohan et al. Zinc iron selenide nanoflowers anchored g-C3N4 as advanced catalyst for photocatalytic water splitting and dye degradation
Wang et al. Rational design of a core–shell-shaped flowerlike Mn 0.05 Cd 0.95 S@ NiAl-LDH structure for efficient hydrogen evolution
Li et al. Noble-metal-free NiS decorated organic-inorganic hybrid ZnxCd1− xSe-diethylenetriamine solid solution for hydrogen evolution
Teymourinia et al. Flower-like nanocomposite of carbon quantum dots, MoS2, and dendritic Ag-based Z-scheme type photocatalysts for effective tartrazine degradation
Hussain et al. Synergetic effect of ZnIn2S4 nanosheets with metal-organic framework molding heterostructure for efficient visible-light driven photocatalytic reduction of Cr (VI)
Li et al. 3D hydrangea‐like InVO4/Ti3C2Tx hierarchical heterosystem collaborating with 2D/2D interface interaction for enhanced photocatalytic CO2 reduction
Chen et al. Construction of CuCd-BMOF/GO composites based on phosphonate and their boosted visible-light photocatalytic degradation
Li et al. Integrating Co3O4 with ZnIn2S4 p‐n heterojunction for efficient photocatalytic hydrogen production
Chu et al. Anti‐Stoke effect induced enhanced photocatalytic hydrogen production

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19707850

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19707850

Country of ref document: EP

Kind code of ref document: A1