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WO2013081550A1 - Photocatalyseur - Google Patents

Photocatalyseur Download PDF

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Publication number
WO2013081550A1
WO2013081550A1 PCT/SG2012/000447 SG2012000447W WO2013081550A1 WO 2013081550 A1 WO2013081550 A1 WO 2013081550A1 SG 2012000447 W SG2012000447 W SG 2012000447W WO 2013081550 A1 WO2013081550 A1 WO 2013081550A1
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WO
WIPO (PCT)
Prior art keywords
photocatalyst
oxide semiconductor
metal oxide
substrate
water
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/SG2012/000447
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English (en)
Inventor
Zuolian CHENG
Yong Tao
Kok Eng TING
Xi Jiang YIN
Dan Shan
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Innomart Pte Ltd
Original Assignee
Innomart Pte Ltd
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 Innomart Pte Ltd filed Critical Innomart Pte Ltd
Priority to CN201280066252.3A priority Critical patent/CN104066510A/zh
Publication of WO2013081550A1 publication Critical patent/WO2013081550A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • 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
    • C02F1/32—Treatment of water, waste water, or sewage by irradiation with ultraviolet light
    • C02F1/325—Irradiation devices or lamp constructions
    • 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
    • B01J23/06—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of zinc, cadmium or mercury
    • 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
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/33—Electric or magnetic properties
    • 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
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/39—Photocatalytic properties
    • 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
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/391—Physical properties of the active metal ingredient
    • B01J35/393—Metal or metal oxide crystallite size
    • 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
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/70—Catalysts, in general, characterised by their form or physical properties characterised by their crystalline properties, e.g. semi-crystalline
    • 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
    • B01J37/08—Heat treatment
    • 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
    • B01J37/12—Oxidising
    • 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
    • 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
    • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
    • 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
    • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
    • B01J2235/15—X-ray diffraction
    • 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
    • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
    • B01J2235/30—Scanning electron microscopy; Transmission electron microscopy
    • 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
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
    • 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
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/301—Detergents, surfactants
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/32—Hydrocarbons, e.g. oil
    • C02F2101/322—Volatile compounds, e.g. benzene
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/34—Organic compounds containing oxygen
    • C02F2101/345—Phenols
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/36—Organic compounds containing halogen
    • C02F2101/363—PCB's; PCP's
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/02—Temperature
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/03—Pressure
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/08—Chemical Oxygen Demand [COD]; Biological Oxygen Demand [BOD]
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/40—Liquid flow rate
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00—General aspects of water treatment
    • C02F2301/08—Multistage treatments, e.g. repetition of the same process step under different conditions
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/04—Disinfection
    • 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
    • C02F2305/02—Specific form of oxidant
    • C02F2305/023—Reactive oxygen species, singlet oxygen, OH radical
    • 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
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00—Technologies for wastewater treatment
    • Y02W10/30—Wastewater or sewage treatment systems using renewable energies
    • Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy

Definitions

  • the present invention generally relates to a photocatalyst.
  • the present invention also relates to a method of producing the photocatalyst, a photocatalytic water treatment system and a method of treating water.
  • Non-destructive processes such as activated carbon adsorption processes and air stripping, Can be used to remove contaminants in wastewater.
  • activated carbon adsorption processes generate hazardous solid wastes which must be disposed off safely.
  • air stripping converts a liquid contaminant in wastewater into a gaseous pollutant .
  • chlorination uses a strong oxidant such as chlorine gas to remove contaminants in wastewater and is thus termed as a "destructive process".
  • chlorination may be hazardous to the health of humans and also to the environment.
  • AOPs advanced oxidation processes
  • UV light ultraviolet
  • AOPs may fully oxidize the target organic contaminants in wastewater to relatively innocuous end products such as carbon dioxide, water and inorganic salts.
  • AOPs do not leave any residual contaminants that require an additional treatment, these processes are well suited for the destruction of organic contaminants .
  • AOPs use compounds such as 0 3 , H 2 0 2 , Ti0 2 and ZnO to generate hydroxyl radicals ( ⁇ 0 ⁇ ) during the oxidation process.
  • ⁇ 0 ⁇ hydroxyl radicals
  • AOPs the efficiency of AOPs depends on factors including the structure of the contaminants, which in turn determines the mechanism of destruction and formation of intermediates, the pH of the wastewater, the design of the photoreactor and the presence of ⁇ 0 ⁇ scavengers such as HC0 3 ⁇ .. Furthermore, AOPs require long residence times to destroy some organic contaminants .
  • the photocatalytic oxidation of the Ti0 2 or ZnO semiconductor absorbs UV light and generates ⁇ radicals mainly from the adsorbed water or OH " ions.
  • the overall oxidation is mainly limited by 0 2 reduction at cathodic sites on the semiconductor surface.
  • Other factors affecting the degradation efficiency are the semiconductor surface area, catalytic properties of the semiconductor and the electron/hole recombination.
  • ZnO as a photocatalyst
  • a number of methods have been proposed for the use of ZnO as a photocatalyst , including suspending ZnO nanoparticles in wastewater.
  • suspending ZnO nanoparticles in wastewater Even with the suspension of ZnO nanoparticles in a slurry photocatalytic reactor, even with low to medium concentrations of ZnO nanoparticles, it is difficult to control uniform irradiation of UV light on the suspension of ZnO nanoparticles.
  • a photocatalyst comprising metal oxide semiconductor nanoparticles in crystalline form integrally formed on the surface of a substrate made of the corresponding metal.
  • the integrally formed metal oxide semiconductor nanoparticles do not give rise to secondary contamination of the treated water. Without being bound by theory, it is believed that by being integrally formed, the metal oxide nanoparticles are resistant to being sloughed off due to abrasive forces.
  • the metal oxide semiconductor may be selected from the group consisting of ZnO, Ti0 2 , Sn0 2 , W0 3 , Fe 2 0 3 , Bi 2 0 3 , Mo0 3 , Zr0 2 and Nb 2 0 5 .
  • the metal oxide semiconductor is ZnO.
  • ZnO is insoluble and non-toxic. Further, ZnO has a powerful oxidizing ability and its ground state electrons are capable of being excited by- absorbing photons from UV radiation. A photocatalytic water treatment system utilizing ZnO activated by UV radiation thus achieves high degradation efficiency of the contaminants that are present in the wastewater. Further advantageously, ZnO is able to degrade or mineralize a wide spectrum of contaminants present in wastewater and also air-borne contaminants. Such contaminants may be for example phenols, cathecol, naphthol, chlorophenols , polychlorinated biphenyls (PCBs) , benzene, benzoic acid and . salicylic acid. Moreover, ZnO may effectively photocatalytically degrade surfactants frequently used in industries .
  • PCBs polychlorinated biphenyls
  • a method of producing a photocatalyst comprising the steps of: a. providing a substrate of a transition metal; b. oxidizing the metal substrate under conditions to integrally form metal oxide semiconductor nanoparticles in crystalline form thereon.
  • the disclosed method is relatively simple and is easily scalable.
  • the photocatalyst produced by the disclosed method has a relatively lower energy transmittance than photocatalysts produced by prior art processes. Accordingly, lesser energy from the light source is transmitted away from the photocatalyst, resulting in more energy being utilized for the photocatalytic activity of the photocatalyst. Thus, the photocatalyst produced by the disclosed method has a higher efficiency in utilizing the energy from the light source.
  • the photocatalyst produced by the disclosed method has a relatively higher specific surface area, thereby increasing the area for contact with wastewater and increasing the efficacy of subsequent mineralization/degradation of the organic contaminants present in wastewater.
  • the method further comprises a step of thermally treating the oxidized substrate to activate the metal oxide semiconductor nanoparticles formed thereon.
  • the thermal treatment step increases the crystallinity of the metal oxide semiconductor nanoparticles formed on the surface of the substrate.
  • the increased crystallinity has been found to increase the photdcatalytic activity of the photocatalysts .
  • a photocatalytic water treatment system having a treatment zone comprising: a plurality of stages, wherein each stage comprises a photocatalyst comprising metal oxide semiconductor nanoparticles in crystalline form integrally formed on the surface of a substrate made of the corresponding metal and wherein each stage further comprises a light source.
  • the plurality of stages provides increased surface area for contact between the photocatalysts and wastewater present in the treatment zone.
  • the plurality of stages further promotes the mineralization/degradation of persistent organic contaminants present in the wastewater by increasing the residence time of wastewater in the photocatalytic water treatment system and the contact between the photocatalyst and the wastewater.
  • each stage is characterized by at least one light source disposed substantially between the photocatalyst of that stage and a photocatalyst of an adjacent stage.
  • the light source and the at least two photocatalysts define a flow path for the contaminated feed water to flow therethrough.
  • the flow path of the feed wastewater traces the perimeter of the at least one light source and the at least two photocatalysts .
  • the flow path of the feed water in each stage is of a substantially U- shape, such that the flow is in a countercurrent direction within a single stage.
  • the light source may be arranged to substantially irradiate at least one exposed planar surface of the photocatalytic substrate.
  • the light source is arranged in between two photocatalytic planar substrate surfaces to thereby irradiate the top surface of one photocatalytic planar substrate and the bottom surface of the other photocatalytic planar substrate.
  • such an arrangement allows the light source to irradiate substantially the entire exposed surface of the planar substrate, thereby achieving uniform irradiation across the substrate surface.
  • the uniform irradiation provides an increased degradation or mineralization of the contaminants present in the wastewater.
  • a method of treating water containing organic contaminants comprising: irradiating a photocatalyst comprising metal oxide semiconductor nanoparticles in crystalline form integrally formed on the surface of a substrate made of the corresponding metal with a light source to activate the metal oxide semiconductor nanoparticles; and contacting said water with the activated metal oxide semiconductor nanoparticles to thereby produce water containing relatively less organic contaminants .
  • integrally formed is to be interpreted broadly to refer to a first element/feature extending or transiting in a continuous manner from a second element/feature as a unitary whole and not as two separate and distinguishable elements.
  • semiconductor is to be interpreted in its broadest sense to refer to materials that are not conductors in its natural state but may easily be excited into a state of conduction.
  • transition metal refers to elements with electrons in a “d” or “f” orbital and. in particular, elements of groups III-XII of the Periodic Table as well as lanthanides and actinides.
  • nano and the term “nanoparticle” as used in the context of the specification is to be interpreted broadly to, unless specified, refer to an average particle size of between about 1 nm to about 1000 nm, specifically between about 1 nm to about 100 nm.
  • the prefix “macro” as - used in the context of the specification is to be interpreted broadly to, unless specified, refer to an average particle size of between about 1 ⁇ to about 1000 tm, and preferably between about 10 ⁇ to 100 ⁇ .
  • the particle size may refer to the diameter of the particles where they are substantially spherical.
  • the particles may be non- spherical and the particle size range may refer to the equivalent diameter of the particles relative to spherical particles or may refer to a dimension (length, breadth, height or thickness) of the non-spherical particle.
  • the word “substantially” - does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.
  • the term "about”, in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.
  • a photocatalyst comprising metal oxide semiconductor nanoparticles in crystalline form integrally formed on the surface of a substrate made of the corresponding metal .
  • the metal of the substrate may be a transition metal.
  • the metal of the substrate is selected from the group consisting of Zn, Ti, Sn, W, Fe, Bi, Mo, Zr and Nb.
  • the corresponding metal oxide semiconductor nanoparticles may be integrally formed from and on the substrate metal.
  • the corresponding metal oxide semiconductor nanoparticles may be selected from the group consisting of ZnO, Ti0 2 , Sn0 2 , W0 3 , Fe 2 0 3 , Bi 2 0 3 , Mo0 3 , Zr0 2 and Nb 2 0 5 respectively.
  • the absorption of radiation energy by the metal oxide semiconductor nanoparticles may be exemplified by the diagram in Fig. 13.
  • the photocatalytic degradation of organic compounds or contaminants is based on semiconductor photochemistry.
  • the semiconductor photocatalyst is irradiated by a light source, such as UV radiation or solar radiation, with a wavelength sufficient to displace the electrons of the photocatalyst from the valence band to the conduction band
  • the wavelength of light required is above 387.5 nm.
  • a localized positively charged "hole” is produced and an electron/hole pair is formed on the semiconductor surface.
  • the organic pollutant may then be adsorbed on the surface of the semiconductor photocatalyst, where the electrons of the pollutant fill the positively charged holes, thereby oxidizing the organic pollutant.
  • the organic pollutant may also be oxidized by the HO radicals, which are powerful oxidizing agents.
  • ⁇ 0 ⁇ radicals are generated from the H 2 0 molecules of the wastewater when the displaced electrons of the metal oxide semiconductor returns to the positively charged hole in the valence band, thereby releasing the binding energy of the electron/hole pair.
  • the binding energy released is capable of splitting the H 2 0 molecules into ⁇ radicals and oxidation of the organic pollutant takes place.
  • the metal of the substrate is Zn and the corresponding metal oxide semiconductor nanoparticles are ZnO.
  • ZnO is a direct band gap semiconductor with room temperature energy gap of 3.37 eV, a large exciton binding energy of 60 meV and low power threshold.
  • irradiation with a light beam having a wavelength of less than 390 nm is required to excite ZnO.
  • a light beam having a wavelength of 365 nm may achieve the degradation of chloro-organic molecules completely.
  • the average nanoparticle size may be from about 30 nm to about 100 nm, or about 50 nm to about 100 nm, or about 70 nm to about 100 nm, or about 30 nm to about 70 nm, or about 30 nm to about 50 nm.
  • the crystalline metal oxide semiconductor nanoparticles possess an average particle size of from about 30 nm to about 100 nm.
  • the crystalline metal oxide semiconductor nanoparticles integrally formed on the metal substrate possess high specific surface area which increases the photocatalytic activity of the photocatalyst .
  • the increased photocatalytic activity may be due to the quantum size effect of the nanoparticles.
  • the quantum size effect refers to the unusual properties exhibited by extremely small crystals that arise from the confinement, of electrons to small regions of space. Due to the quantum size effect of the nanoparticles, the band gap between the highest valence band and the lowest conduction band increases with a decrease in size of the nanoparticles. Thus, more energy is needed to excite the electrons of the nanoparticles and more energy is also released when the nanoparticles return to their ground state. Accordingly, the increase in the band gap increases the redox capabilities of the electron/hole pair of the excited nanoparticles, thereby increasing the photocatalytic activity of the nanoparticles.
  • the substrate may be in the form of a sheet or wire or in powder form.
  • metal oxide semiconductor nanoparticles may be integrally formed on both sides of the sheet.
  • metal oxide semiconductor nanoparticles may be integrally formed on one side of the sheet.
  • metal oxide semiconductor nanoparticles may be integrally formed co- axially on the circumference of the wire.
  • the metal oxide semiconductor nanoparticles may be integrally formed on the surface of the powder.
  • the Zn substrate is composed of substantially pure metallic zinc.
  • the substantially pure metallic zinc substrate may possess a purity of about 95% purity of Zn or higher, or about 98% purity of Zn or higher, or about 99% purity of Zn or higher.
  • the substrate is an alloy of zinc and other metals.
  • the substrate is a metal composite material comprising Zn and other inorganic materials, such as, quartz, or ceramic material.
  • the average thickness of the substrate having metal oxide semiconductor nanoparticles integrally formed thereon is from about 0.1 ⁇ to about 1 mm.
  • the metal oxide semiconductor nanoparticles may be formed by oxidizing the metal substrate with an oxidizing agent.
  • the oxidizing agent is a liquid oxidant .
  • a method of producing a photocatalyst comprising the steps of: a. providing a substrate of a transition metal; b. oxidizing the metal substrate under conditions to integrally form metal oxide semiconductor nanoparticles in crystalline form thereon.
  • the liquid oxidant used in the oxidizing step may be any chemical capable of oxidizing the metal substrate.
  • the oxidizing agent may be selected from the group consisting of chlorine, organic chlorines, chlorine dioxide, peroxide, persalt, peracids, persulfates and peroxyphthalates .
  • H 2 0 2 is used as the oxidant in the oxidizing step.
  • the oxidant solution may further comprise a mixture of NaF, NaCl and Na 2 S0 4 .
  • the oxidizing step may be conducted for at least 72 hours.
  • the oxidizing step may be conducted at a temperature from about 60°C to about 80°C.
  • H 2 0 2 decomposes at a temperature from about 60°C to about 80°C to produce strongly oxidizing radicals, which leads to the formation of ZnO nanoparticles on the surface of the Zn substrate .
  • the method further comprises the step of pickling the substrate in a pickling solution to remove contaminants, such as undesirable metal oxides, from the surface of the substrate.
  • the pickling step may be performed before the oxidizing step.
  • the pickling solution may comprise of an acid.
  • the acid is selected from the group consisting of HF, HN0 3 and mixtures thereof.
  • the pickling solution may further comprise of water.
  • the water is deionized water.
  • the pickling solution comprises
  • the HF may have a concentration of about 38 wt% to about 55 wt%, or about 38 wt% to about 50 wt%, or about 38 wt% to about 45 wt%, or about 45 wt% to about 55 wt%, or about 40 wt% to about 50 wt%.
  • the pickling solution comprises of a mixture of HF, HN0 3 and water.
  • the mixture of HF, HN0 3 and water may comprise of HF in the range of about 1 vol% to about 25 vol%, HN0 3 in the range of about 10 vol% to about 50 vol% and water in the range of about 45 vol to about 75 vol%, wherein the volume of HF, HN0 3 and water makes up 100 vol%.
  • the volume ratio of HF : HN0 3 : water is 1:3:6.
  • the pickling step may be conducted at a temperature suitable to remove undesirable particles from the surface of the substrate.
  • the temperature of the pickling step may be in the range of about 15°C to about 30°C, or about 20°C to about 30°C, or about 25°C to about 30°C, or about 15°C to about 25°C, or about 15°C to about 20°C.
  • the pickling step is conducted at ambient temperature (about 15°C to 30°C) .
  • the method may further comprise the step of thermally treating the oxidized substrate to activate the metal oxide semiconductor nanoparticles formed thereon.
  • the thermal treatment step may be performed after the oxidation step.
  • the steps are performed sequentially such that the pickling step is performed before the oxidation step and the thermal treatment step is performed after the oxidation step.
  • the heating rate of the thermal treatment step is from about 5°C/min to about 15°C/min. In another embodiment, the heating rate of the thermal treatment step is about 10°C/min.
  • the maximum temperature attained during the thermal treatment step may be from about 300°C to about 600°C, or from about 400°C to about 600°C, or from about 300°C to about 500°C. In one embodiment, the maximum temperature attained during the thermal treatment step is 450°C.
  • the morphology of the metal oxide semiconductor nanoparticles may be altered by altering the temperature attained during the thermal treatment step. Specifically, the crystallinity and the particle size of the nanoparticles may be altered by altering the temperature attained during the thermal treatment step.
  • the thermal treatment step advantageously increases the crystallinity of the metal oxide semiconductor nanoparticles formed on the surface of the substrate, thereby increasing the photocatalytic activity of the photocatalysts .
  • the crystallinity of nanoparticles may be determined by X-ray diffraction, wherein an increase in crystallinity is characterized by . sharp diffraction peaks due to the reflection of photons off the regularly-spaced crystal structures. On the other hand, crystal structures with low crystallinity exhibit weak, diffuse diffraction peaks.
  • the thermal treatment step may also increase the particle size of the metal oxide semiconductor nanoparticles formed on the surface of the substrate.
  • the specific surface area of the crystals of the metal oxide semiconductor nanoparticles decreases, which may lead to a reduction in photocatalytic activity of the photocatalyst.
  • a maximum temperature of 450°C attained during the thermal treatment step can increase the crystallinity of the metal oxide semiconductor nanoparticles with a minimal decrease of the specific surface area of the crystals, thereby optimizing the photocatalytic activity of the photocatalyst .
  • the metal oxide semiconductor nanoparticles formed by the method defined above possess an average particle size of from about 30 nm to about 100 nm.
  • such nanoparticles possess high specific surface area which increases the photocatalytic activity of the photocatalyst.
  • the crystalline metal oxide semiconductor nanoparticles formed by the method defined above possess relatively lower absorbance than photocatalysts produced by prior art processes.
  • a photocatalytic water treatment system having a treatment zone comprising: a plurality of stages, wherein each stage comprises a photocatalyst comprising metal _ oxide semiconductor nanoparticles in crystalline form integrally formed on the surface of a substrate made of the corresponding metal and wherein each stage further comprises a light source.
  • the disclosed system may comprise of two or more stages. In one embodiment, the system comprises four stages.
  • the metal oxide semiconductor nanoparticles of the plurality of stages may be composed of the same metal oxide or may compose of different metal oxides.
  • the photocatalyst may be supported on a removable frame within the treatment zone.
  • the removable frame may be made of any UV resistant material, such as stainless steel.
  • the frame may be removed from the system for maintenance or cleaning when required.
  • the removable frame may be configured to secure the substrate in place such that at least two planar surfaces of the substrate are exposed for contact with wastewater.
  • the light source may emit a wavelength of light sufficient to excite the metal oxide semiconductor nanoparticles.
  • the light source is a UV light source.
  • the UV light source is solar radiation.
  • the UV light source is a UV lamp.
  • the UV lamp may be any suitable lamp known in the art , such as a xenon lamp or a mercury lamp .
  • the UV lamp used may be a high pressure xenon lamp or a low pressure mercury lamp.
  • the UV lamp used may be a high pressure mercury lamp.
  • the light source may be configured such that the longitudinal axis . through the light source is substantially parallel to the longitudinal axis passing through the substrate of the photocatalyst. In one embodiment, the light source is arranged to substantially irradiate at least one planar surface of said photocatalyst. In another embodiment, the light source is arranged to substantially irradiate at least two planar surfaces. In yet another embodiment, the flow path substantially traces the perimeter of the photocatalysts and the . light source.
  • the flow path of the wastewater is made to flow substantially along the perimeter of the photocatalyst and the ligh source, thereby maximizing the contact of the wastewater with the photocatalyst whilst concurrently illuminating the entire length of the flow path as the wastewater contacts the photocatalyst .
  • the light source and the photocatalyst of each stage may be configured such that the flow of wastewater in the treatment zone is in a countercurrent direction.
  • the flow of the contaminated feed water may be in a substantially parallel direction to the longitudinal axes of the substrate and the light source.
  • the contact of the feed water with the photocatalyst and the light source may be maximized.
  • the photocatalysts and the light sources are arranged alternately to thereby define a substantially U-shaped flow path in each stage for the contaminated feed water - to flow therethrough.
  • the contaminated water may flow between the photocatalyst and the light source in a U-shaped flow path in each stage of the photocatalytic reactor.
  • the flow of the feed water within the treatment zone is in a countercurrent direction.
  • the contact of the feed water with the photocatalyst and the light source may be maximized.
  • the light source may be enclosed by a cover within the treatment zone.
  • the cover may be made of any suitable material able to withstand the conditions within the treatment zone.
  • the cover may be made of any UV resistant material that also allows light to pass through.
  • the cover is made of quartz.
  • the cover may be equipped with a switch to operate the light source.
  • the switch may include a safety feature that automatically switches the light source off when the cover is open.
  • the treatment zone of the photocatalytic water treatment system may be enclosed by a container.
  • the container may be made of any UV resistant material, such as stainless steel.
  • the container enclosing the treatment zone may be sized according to the requirements of the water treatment process.
  • the container enclosing the treatment zone may also be sized according to the number of stages in the system.
  • the container has a capacity of 50 liters.
  • the system may comprise of sensors placed within the treatment zone so that the process may be monitored in real time.
  • the sensors may monitor the temperature and/or the pressure in the treatment zone.
  • the system may further comprise a flow rate limiter to adjust the flow rate of contaminated water entering the treatment zone.
  • the flow rate limiter may be a flow meter.
  • the flow rate limiter may be used as a safety measure to limit the flow rate to a predetermined maximum allowable value.
  • the flow rate limiter may also advantageously control the residence time of the contaminated feed water.
  • the system may comprise of a tank to store contaminated feed water.
  • the tank may be of any suitable size.
  • the tank may also be made of any suitable material capable of containing contaminated feed water.
  • a filtration membrane may be provided in the tank.
  • the filtration membrane may be any suitable porous membrane capable of removing contaminants in the contaminated feed water.
  • the filtration membrane may be used to remove suspended particles in the contaminated feed water before being treated in the treatment zone .
  • the filtration membrane may also be used to remove particles resulting from the degradation of organic contaminants in the treatment zone.
  • the pores of the filtration membrane are micro-sized.
  • Sensors may be provided in the tank for real time monitoring.
  • An example of a sensor that may be provided in the tank is a sensor that monitors the chemical oxygen demand (COD) of the water in the tank.
  • COD chemical oxygen demand
  • the system may also comprise a pump to pump the feed water into the treatment zone .
  • the pump may be capable of providing variable feed flow rates suitable for operation of the water treatment system. In one embodiment, the pump delivers a flow rate of about 100 mL/min to about 1000 mL/min.
  • the pump may also permit the system to be capable of recirculating the feed water. Exemplary, non-limiting embodiments of a method of treating water containing organic contaminants according to the fourth aspect will now be disclosed.
  • a method of treating water containing organic contaminants comprising: irradiating a photocatalyst comprising metal oxide semiconductor nanoparticles in crystalline form integrally formed on the surface of a substrate made of the corresponding metal with a light source to activate the metal oxide semiconductor nanoparticles; and contacting said water with the activated metal oxide semiconductor nanoparticles to thereby produce water containing relatively less organic contaminants .
  • the feed water containing organic contaminants may have more than about 50% of the contaminants degraded to produce treated water. In one embodiment, the water containing organic contaminants has more than 75% of the contaminants degraded. In another embodiment, the water containing organic contaminants has more than 85% of the contaminants degraded. In yet another embodiment, the water containing organic contaminants has more than 95% of the contaminants degraded.
  • the pH of the feed water may be adjusted before treatment. In one embodiment, the pH of the feed water is adjusted between about 6 to about 9. In another embodiment, the pH of the feed water is adjusted to 7.5.
  • the method may further comprise a step of removing suspended particles from the feed water before contacting the feed water with the activated metal oxide semiconductor nanoparticles.
  • the removing step comprises membrane filtration.
  • the membrane may be any suitable micro-sized, porous membrane for removing the mineralized contaminants.
  • Figs. la and lb shows field emission scanning electron microscope (FE-SEM) micrographs of the ZnO nanoparticles formed on the surface of .
  • Fig. 2 shows the energy dispersive spectrum (EDS) of the integrally formed ZnO nanoparticles obtained from Example 1.
  • Fig. 3 shows the FE-SEM micrograph of the commercial ZnO nanoparticles used in ⁇ Comparative Example 1 at 40, OOOx magnification.
  • Fig. 4 shows the FE-SEM micrograph of the Zn sheets printed with ZnO nanoparticles obtained from Comparative Example 1 at 40, OOOx magnification.
  • Fig. 5 shows a schematic diagram of a four-stage photocatalytic water treatment system used in Example 13.
  • Fig. 6 shows a schematic diagram of a four-stage photocatalytic water treatment system powered using solar energy.
  • Figs. 7a, 7b and 7c show graphs of the degradation efficiency of the photocatalytic water treatment system of Example 13 to degrade phenol with initial concentrations of 5 ⁇ g/mL ( 10 /xg/mL and 20 ⁇ g/mL respectively versus irradiation time.
  • Fig. 8 shows a graph of the natural logarithm of normalized initial concentrations of 5 g/mL, 10 ⁇ g/mL and 20 ⁇ g/mL of phenol in Example 13 versus irradiation time.
  • Fig. 9 shows a graph of the degradation efficiency of the photocatalytic water treatment system of Example 14 to degrade phenol with an initial concentration of 10 ⁇ g/mL in the different pH solutions versus irradiation time.
  • Fig. 10 shows the effect of pH value on the apparent rate constant ( ⁇ 3 ⁇ ) of Example 14.
  • Fig. 11 shows a graph of the discoloration efficiency of the photocatalytic water treatment system of Example 16 to degrade Rhodamine B (RB) having an initial concentration of 15 ⁇ g/mL.
  • Fig. 12 shows a UV-Vis absorption spectrum of the discoloration efficiency of the photocatalytic water treatment system of Example 15 to degrade RB with and without the ZnO photocatalyst .
  • the . average particle diameter was determined by repeatedly determining the average volume of 20 particles taken at from a random field of view in a field emission scanning electronic microscope (FE-SEM, JEOL Ltd., Japan).
  • the mean film thickness was determined by stylus surface profilometer (DEKTA 6M, Veeco Company, New York, United States of America) .
  • the absorbance of the samples thereof was determined at 275 nm to 400 nm by UV-Vis spectrometer (UV-1800, Shimadzu Corporation, Japan) to evaluate the light transmittances in the ultraviolet and visible ray region.
  • Zn sheets purchased from Titan Engineering Pte Ltd, Singapore (99.5% in purity) with a size of 2.5 cm x 2.0 cm x 0,1 cm were pickled in a pickling solution consisting of concentrated HF, concentrated HN0 3 and deionized water with a volume ratio of 1:3:6 at ambient temperature.
  • each piece of Zn sheet was oxidized in 50 ml of an oxidant solution of 30 wt% H 2 0 2 and subjected to a first step of thermal treatment by heating at 80°C in an oven for 72 hours to produce ZnO nanoparticles formed on each Zn sheet.
  • the Zn sheets were then removed from the oven, rinsed with deionized water and dried in air.
  • the Zn sheets were then subjected to a second step of thermal treatment, which was conducted in a furnace at a heating rate of 10°C/min to attain the designated temperature of 450°C. The temperature was maintained for 1 hour, followed by furnace cooling to ambient temperature.
  • Figs, la and lb The FE-SEM micrographs of the ZnO nanoparticles integrally formed on the surface of the Zn sheets is shown in Figs, la and lb. It can be seen that the nanoparticles formed have smaller average particle sizes and thus have a larger specific surface area.
  • the energy dispersive spectrum of the integrally formed ZnO nanoparticles can be seen from Fig. 2.
  • the oxygen atom has 898.39 wt% and 60.88 atomic%, while the Zinc atom has 2358.97 wt% and 39.12 atomic%.
  • Example 1 The procedure described in Example 1 was repeated except that different substances were added to the oxidant solution.
  • the different substances added are described, in Table 1 below.
  • the paste was printed by a 136 ⁇ sieved screen on zinc sheets with a size of 2.5cm x 2.0cm x 0.1cm, to obtain deposited layers of 50 g/m 2 .
  • the printed sheets were then calcined at 300°C to remove .the organic solvents used in the paste preparation.
  • the properties of the zinc sheets printed with ZnO nanoparticles were determined in the same way as in Examples 1 to 9.
  • the FE-SE micrograph of the commercial ZnO nanoparticles is shown in Fig. 3 and the FE-SEM micrograph of the zinc sheets printed with ZnO nanoparticles obtained from Comparative Example 1 is shown in Fig. 4. It can be seen that the crystals of the commercial ZnO nanoparticles and that of the ZnO nanoparticles obtained from Comparative Example 1 is larger in average size and is less uniform than those obtained from Examples 1 to 9. Specifically, the average particle size of the screen-printed ZnO nanoparticles is about 70 to 120nm.
  • the commercial ZnO nanoparticles and the ZnO nanoparticles screen-printed on zinc sheets possess larger average particle sizes, these nanoparticles possess a smaller specific surface area.
  • the specific surface area of the screen-printed ZnO nanoparticles is about 46 m 2 /g.
  • T%) percentage of transmittance
  • Example 2 The procedure described in Example 1 was repeated except that a larger zinc sheet is used in this example.
  • the zinc sheet used in this example is 15cm x 12.5cm x 0.1 cm.
  • Example 10 The properties of the ZnO nanoparticles obtained from Example 10 are similar to that of Example 1. Hence, the properties of the ZnO nanoparticles are not dependent on the size of the metallic substrate.
  • Example 10 The procedure described in Comparative Example 1 to obtain ZnO nanoparticles screen-printed on a zinc sheet was repeated except that a larger zinc sheet is used in this example.
  • the zinc sheet used in this example is 15cm x 12.5cm x 0.1 cm.
  • the properties of the ZnO nanoparticles obtained from Example 10 are similar to that of Example 1. Hence, the properties of the ZnO nanoparticles are not dependent on the size of the metallic substrate.
  • Example 1 The procedure described in Example 1 was repeated except that the designated temperature of the thermal treatment step attained is 450°C and 700°C respectively.
  • the crystal structure of the ZnO nanoparticles integrally formed on the surface of the Zn sheets obtained from Examples 11 and 12 are similar to that of Example 1.
  • the photocatalytic activity was calculated by the photocatalytic degradation of rhodamine B (RB) .
  • the ZnO nanoparticles obtained from Example 1 has the highest specific surface area and the smallest particle size.
  • the particle size slightly increased, leading to a decrease in specific surface area.
  • the temperature of the thermal treatment step increased to 700°C, the particle size increased and the specific surface area decreased dramatically.
  • ZnO nanoparticles integrally formed on the surface of zinc sheets obtained from Example 11 retained their small grain size and high specific surface area when the temperature of the thermal treatment step increased up to a temperature of 450°C.
  • the ZnO nanoparticles integrally formed on the surface of the Zn sheets obtained from Example 1 were used in a four-stage photocatalytic water treatment system 100 shown in Fig. 5 in accordance with an embodiment of the invention.
  • the four-stage photocatalytic water treatment system 100 is fitted with four pieces of Zn sheets 106 having ZnO nanoparticles integrally formed thereon as the photocatalyst .
  • the Zn sheets 106 are supported by a removable frame 108.
  • Eight ultraviolet-C (UVC) lamps 102 with 9 w are used as the irradiation source and the lamps 102 are each protected with a quartz cover 104 within container 114.
  • Lamps 102 are also covered at one end with covers 115 which are equipped with a safety switch (not shown) . The safety switch will automatically switch off the " UV lamps 102 when covers 115 are open.
  • Covers 115 may also provide connection to a power supply (not shown) and a data processing system (not shown) .
  • a single sheet 106 and two lamps 102 form a stage 116.
  • the sheets 106 and lamps 102 are arranged parallel to each other so that contact of a solution containing contaminants with the sheets 106 and lamps 102 is maximized.
  • the system 100 is enclosed by container 114 that is able to hold 50 L of phenol solution.
  • the flow rate of pump 110 may be adjusted and is adjusted to 16.8 L/hr in the following examples unless otherwise stated.
  • the phenol solution from tank 112 flows through pump 110 into flow rate limiter 120 and into system 100.
  • Tank 112 may be divided into two compartments by a micro-sized porous membrane 118.
  • Membrane 118 is used to remove suspended particles present in the solution in tank 112.
  • the flow of the phenol solution in system 100 follows arrow A in a U-shaped direction, so that the flow of the solution passing through each stage 116 is in a countercurrent direction. The flow may then be recirculated back to tank 112 to be pumped back to system 100 for further treatment.
  • a four-stage photocatalytic water treatment system 200 powered by solar energy is shown in Fig. 6. Like numbers denote like parts.
  • Contaminated water from tank 212 having a porous membrane 218 is pumped by pump 210 through flow rate limiter 220 into system 200.
  • each stage 216 comprises a photocatalyst and UV lamps (not shown) .
  • UV lamp covers 215 are linked via wires 222 to a data processing system 224 with a power supply 226.
  • Power supply 226 comprises a solar panel 228, an accumulator 230 and a controller 232. Power supply 226 obtains solar energy from the sun via solar panel 228 to power system 200. Thus, minimum energy cost is required to run system 200.
  • the four-stage photocatalytic water treatment system 100 shown in Fig. 5 was used to treat a phenol solution which is used as an exemplary water contaminant .
  • the pH of the phenol solution was adjusted to pH 7 by adding HC1.
  • Different initial concentrations of phenol solution was passed through the system 100.
  • the degradation efficiency of the system 100 to degrade phenol having initial phenol concentrations of 5 g/mL, 10 ⁇ g/mL and 20 ⁇ g/mL is shown in the graphs in Figs. 6a to 6c respectively when the UV lamp 102 was switched off (without UV) and when the UV lamp 102 was switched on (with UV) .
  • Example 13 The procedure described in Example 13 was repeated except that phenol solutions with a pH value of pH 2, pH 3, pH 6, pH 7.5 and pH 9 were used. Further, the initial concentration of phenol was fixed at 10 ⁇ / ⁇ . The results obtained are shown in Fig. 8.
  • Rhodamine B is one of the most important xanthene dyes and is famous for its good stability. Thus, the treatment of effluents containing such dye compounds is important. Degradation of RB was carried out in a four-stage photocatalytic water treatment system 100 shown in Fig. 5 in order to study the degradation efficiency of a moderate initial concentration of RB. The degradation of RB is characterized by its discoloration.
  • Example 13 The procedure described in Example 13 was repeated except that the initial concentration of RB was fixed at 15 pg/mL.
  • Example 13 The procedure described in Example 13 was repeated except that a bisphenol A (BPA) solution having an initial concentration of 5 g/mL was used. Further, the flow rate of the pump was adjusted to 120 mL/min. In this example, the degradation efficiency of BPA is more than 9.0%.
  • BPA bisphenol A
  • the disclosed photocatalyst comprising metal oxide semiconductor nanoparticles in crystalline form integrally, formed on the surface of a substrate made of the corresponding metal , when used in a water treatment system, does not give rise to secondary contamination of the treated water.
  • the metal oxide semiconductor nanoparticles disclosed herein may be able to degrade or mineralize a wide spectrum of contaminants present in wastewater and also air-borne contaminants, such as phenols, cathecol, naphthol, chlorophenols, polychlorinated biphenyls (PCBs) , benzene, benzoic acid, salicylic acid and surfactants.
  • contaminants such as phenols, cathecol, naphthol, chlorophenols, polychlorinated biphenyls (PCBs) , benzene, benzoic acid, salicylic acid and surfactants.
  • the photocatalyst produced by the disclosed method may possess a relatively high specific surface area, thereby increasing the degradation or mineralization of organic contaminants present in wastewater.
  • the disclosed method may comprise a thermal treatment step which advantageously increases the crystallinity of the metal oxide semiconductor nanoparticles formed on the surface of the substrate, thereby increasing the photocatalytic activity of the photocatalysts.
  • the disclosed photocatalytic water treatment system may comprise a plurality of stages that increases the extent of the mineralization of persistent organic contaminants present in the wastewater.
  • the flow of wastewater in the treatment zone may be in a countercurrent direction so that contact between the wastewater and the photocatalyst may be maximized.
  • the light source may be configured to uniformly irradiate the photocatalyst to provide an increased degradation or mineralization of the contaminants present in the wastewater.
  • more than about 50% of the organic contaminants present in the feed water may be degraded. In one embodiment, more than about 95% of the organic contaminants present in the feed water may be degraded.

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Abstract

La présente invention concerne un photocatalyseur comprenant des nanoparticules semi-conductrices à base d'oxyde métallique sous forme cristalline formées d'un seul tenant sur la surface d'un substrat fait du métal correspondant, et un procédé de fabrication de ce photocatalyseur. L'invention concerne également un système de traitement de l'eau photocatalytique ayant une zone de traitement comprenant : une pluralité d'étages, chaque étage comprenant un photocatalyseur comprenant des nanoparticules semi-conductrices à base d'oxyde métallique sous forme cristalline formées d'un seul tenant sur la surface d'un substrat fait du métal correspondant et chaque étage comprenant une source de lumière.
PCT/SG2012/000447 2011-11-29 2012-11-28 Photocatalyseur Ceased WO2013081550A1 (fr)

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CN109590026A (zh) * 2018-11-30 2019-04-09 河海大学 一种复合光催化材料及其制备方法和应用
CN113198455A (zh) * 2021-05-17 2021-08-03 南昌航空大学 一种三氧化钼/钼网光催化剂及其制备方法和应用

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