WO2013093805A1 - Method of reducing contaminants in water - Google Patents

Method of reducing contaminants in water Download PDF

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Publication number
WO2013093805A1
WO2013093805A1 PCT/IB2012/057487 IB2012057487W WO2013093805A1 WO 2013093805 A1 WO2013093805 A1 WO 2013093805A1 IB 2012057487 W IB2012057487 W IB 2012057487W WO 2013093805 A1 WO2013093805 A1 WO 2013093805A1
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WIPO (PCT)
Prior art keywords
preparing
nanotubular
composite matrix
water
matrix
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PCT/IB2012/057487
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French (fr)
Inventor
Thembele Kenneth HILLIE
Lucky Mashudu SIKHWIVHILU
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Csir
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Publication of WO2013093805A1 publication Critical patent/WO2013093805A1/en

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    • 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
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/063—Titanium; Oxides or hydroxides thereof
    • 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
    • B01J23/48—Silver or gold
    • B01J23/50—Silver
    • 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
    • B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain 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
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • 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
    • B01J37/009—Preparation by separation, e.g. by filtration, decantation, screening
    • 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
    • B01J37/0201—Impregnation
    • 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
    • B01J37/06—Washing
    • 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
    • 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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • 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
    • C02F1/50—Treatment of water, waste water, or sewage by addition or application of a germicide or by oligodynamic treatment
    • C02F1/505—Treatment of water, waste water, or sewage by addition or application of a germicide or by oligodynamic treatment by oligodynamic treatment
    • 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

Definitions

  • the present invention relates to a method and matrix for reducing contaminants in water and to a method for preparing such a matrix.
  • halogens such as chlorine (CI) and bromine (Br) are well known and widely used as antibacterial agents, but the direct use of these halogens as antibacterial agents has many disadvantages, because of their high toxicity and high vapour pressure in pure form.
  • Another disadvantage associated with the use of halogens is that they may potentially react with other chemical contaminants to form by-products that could be carcinogenic.
  • US2712573 One of the disadvantages disclosed in US2712573 is that the method for water purification uses irradiation from an electric light bulb having a specific spectrum of 200 nm to 400 nm. In addition, U32712573 is limited only to the contaminated water exposed to such spectrum of ultraviolet radiation. A further disadvantage is that the method requires a reliable source of electricity and light, without any risk of interruption.
  • the intensity may be insufficient to completely inactivate the most UV- resistant microorganisms, such as adenoviruses.
  • US20100032353 discloses a liquid dispenser or water purification unit having a housing and a mouthpiece configured for contact with the mouth of a person. At least part of the mouthpiece is provided with an antimicrobial surface coating comprising silver nanoparticles complexed with titanium dioxide.
  • a disadvantage associated with US20100032353 is that the filter embedded in the unit lasts only a year, (approximately 700 liters) meaning users must replace the unit annually.
  • a further disadvantage is that the antimicrobial surface is not used for water purification, but to ensure that bacteria from one person holding or drinking from the mouthpiece are killed on contact with the antimicrobial, such that a second person using the mouthpiece is not infected by the bacteria.
  • a nanotubular composite matrix for reducing contaminants in water comprising a photocatalytic agent in nanotubular form loaded with an antimicrobial agent.
  • the photocatalytic agent is a body of titanium dioxide (Ti0 2 ) nanotubes.
  • the nanotubes may have a cross- sectional diameter of from 2 nm to 200 nm, preferably 7 nm to 1 1 nm.
  • the antimicrobial agent is a body of silver (Ag) particles.
  • the particles may have a cross-sectional diameter of from 0.5 nm to 30 nm, preferably 1 nm to 5 nm.
  • a method for preparing a nanotubular composite matrix for reducing contaminants in water and on the matrix ' s surface including the steps of:
  • the step of preparing the photocatalytic agent in the form of titanium dioxide may include the step of adding the titanium dioxide in an alkali salt to form a mixture, wherein the alkali salt may have a concentration of at least 2 M, preferably from 5 M to 30 M.
  • the titanium dioxide in the mixture may be selected in the range of from 2% to 50% (w/v), preferably from 10% to 30% (w/v).
  • the alkali salt may be selected from the group consisting of potassium hydroxide, sodium hydroxide, and calcium hydroxide.
  • the step of preparing the photocatalytic agent may include the further step of stirring the mixture at an elevated temperature of up to 300 degrees Celsius for up to 24 hours to form titanium dioxide nanotubes. Furthermore, the step of preparing the photocatalytic agent may include the further step of centrifuging the mixture to separate the nanotubes from the alkali salt.
  • the step of preparing the photocatalytic agent may include the further step of washing the nanotubes with deionised water to remove excess alkali salt from the nanotubes and to maintain conductivity of the nanotubes constant below 100 pS/cm.
  • the step of preparing the photocatalytic agent may include the further step of drying the nanotubes at a temperature up to 200 degrees Celsius for at least 2 hours, preferably at 120 degrees Celsius for 12 hours and subsequently at 25 degrees Celsius for 5 hours.
  • the step of preparing the photocatalytic agent may include the further step of sieving the nanotubes having an external diameter of from 2 nm to 200 nm, preferably from 7 nm to 1 1 nm, in accordance with the first aspect of the invention.
  • the step of dissolving the antimicrobial agent in the solvent may include the step of selecting the solvent from the group consisting of organic solvents and inorganic solvents, preferably inorganic solvents, further preferably deionised water.
  • the step of dissolving the antimicrobial agent in the solvent may further include the antimicrobial agent having a concentration in the range of from 0.1 % to 15% (w/v), preferably 0.5% to 7% (w/v).
  • the step of loading the photocatalytic agent with the antimicrobial agent may include the step of mixing the dried nanotubes with the antimicrobial agent in solution to form the matrix.
  • the step of removing the excess solvent from the matrix may include the step of incubating the matrix at a temperature up to 250 degrees Celsius for at least 10 hours, preferably at 25 degrees Celsius for 24 hours and subsequently at 120 degrees Celsius for 24 hours.
  • the step of calcining the matrix to remove the moiety of the antimicrobial agent may include the step of elevating the temperature up to 1000 degrees Celsius for at least 5 hours, preferably 300 degrees Celsius for 12 hours to form the nanotubular composite matrix of the first aspect of the invention.
  • the moiety of the antimicrobial agent is nitrate (N0 3 ).
  • a method for reducing contaminants in water including the steps of:
  • the light source may be selected from the group consisting light buib or sunlight, preferably sunlight.
  • a device for reducing contaminants in water comprising:
  • nanotubular composite matrix according to the first aspect of the invention disposed within the container.
  • the container is of a translucent material to allow light to pass through the container to activate a photocatalytic agent.
  • the container is provided with a light source.
  • Figure 1 is a graph depicting the fraction of survivors of Escherichia coli (£. coli) culture incubated with a nanospherical composite matrix at varying concentration when a photocatalytic agent is exposed to ultraviolet radiation from sunlight for 90 minutes;
  • Figure 2 is a graph depicting the fraction of survivors of £. coli culture incubated with a nanorod composite matrix at varying concentration when a photocatalytic agent is exposed to ultraviolet radiation from sunlight for 90 minutes; and
  • Figure 3 is a graph depicting the fraction of survivors of E. coli culture incubated with a nanotubular composite matrix according to a preferred embodiment of the invention at varying concentration when a photocatalytic agent is exposed to ultraviolet radiation from sunlight for 90 minutes.
  • a method for preparing a nanotubular composite matrix for reducing contaminants in water and on the matrix ' s surface includes the steps of:
  • - preparing a photocatalytic agent comprising titanium dioxide in nanotubular form to form titanium dioxide nanotubes - dissolving an antimicrobial agent in the form of silver nitrate having a concentration of between 0.1 % to 15% (w/v), preferably 0.5% to 7% (w/v), further preferably 3.4% in an inorganic solvent, such as deionised water;
  • ⁇ removing excess solvent from the matrix by incubating the matrix at a temperature of up to 250 degrees Celsius for at least 10 hours, preferably at 25 degrees Celsius for 24 hours and subsequently at 120 degrees Celsius for 24 hours;
  • the step of preparing the photocatalytic agent in the form of titanium dioxide includes the step of adding the titanium dioxide in an alkali salt to form a mixture, wherein the alkali salt may have a concentration of at least 2 M, preferably from 5 M to 30 M.
  • the step of preparing the photocatalytic agent includes the step of stirring the mixture at an elevated temperature of up to 300 degrees Celsius for at least 12 hours, preferably 150 degrees Celsius for 24 hours to form the titanium dioxide nanotubes.
  • the step of preparing the photocatalytic agent includes the further step of centrifuging the mixture to separate the nanotubes from the alkali salt.
  • the step of preparing the photocatalytic agent includes the further step of washing the nanotubes with deionised water to remove excess alkali salt from the nanotubes and to maintain conductivity of the nanotubes constant below 100 pS/cm.
  • the step of preparing the photocatalytic agent includes the further step of drying the nanotubes at a temperature up to 200 degrees Celsius for at least 2 hours, preferably at 120 degrees Celsius for 12 hours and subsequently at 25 degrees Celsius for 5 hours.
  • the step of preparing the photocatalytic agent includes the further step of sieving the nanotubes.
  • the nanotubes have a cross- sectional diameter of from 2 nm to 200 nm, preferably 7 nm to 1 1 nm.
  • the first step of the method is to prepare the titanium dioxide in a nanotubular form.
  • other forms of the titanium dioxide such as nanorod and nanospherical, were also prepared from a commercial P25 Degussa titania to establish which form of titanium dioxide is capable of reducing contaminants in water.
  • the titanium dioxide nanotubes about 23 g of the Degussa titania powder is placed in a teflon container together with 150 ml of 18 M potassium hydroxide to form a mixture. The mixture is stirred at a constant rate of 500 rpm in an autoclave at a temperature of 150 degrees Celsius for 24 hours.
  • the mixture is stirred at a constant rate of 500 rpm in a microwave reactor for 5-10 minutes.
  • the mixture is allowed to cool at room temperature for 24 hours to form titanium dioxide nanotubes.
  • the nanotubes are separated from the mixture by centrifugation at a stirring rate of 10 000 rpm for 30 minutes at 4 degrees Celsius.
  • the nanotubes are again washed with deionised water to remove excess potassium hydroxide from the nanotubes and to maintain conductivity of the nanotubes constant below 100 pS/cm. It was noted that removal of the alkali salt from the nanotubes could take at least a week.
  • the nanotubes are dried in an oven at 120 degrees Celsius for 12 hours and then allowed to cool to room temperature for 5 hours.
  • the nanotubes are then sieved to a desired size.
  • the nanotubes have a cross-sectional diameter of from 7 nm to 1 1 nm.
  • the above method is also followed when preparing the titanium dioxide in a nanorods form but 10 M of potassium hydroxide is used instead.
  • the titanium dioxide in a nanospherical form is prepared by using the above commercial P25 Degussa titania powder. Firstly, the powder is modified and then used. The modification is achieved by mixing the powder with water and then compressed into a moist paste. This moist paste is then dried in an oven at 120 degrees Celsius for 48 hours to form the titanium dioxide nanospheres. The nanospheres are cooled and crushed into fragments. The fragments having the desired size of the nanospherical form are sieved out. The larger fragments are recycled and re-sieved while the smaller ones (fine powder formed as a result of crushing) are mixed with water again to from the moist paste.
  • the silver nitrate is prepared and loaded to the nanotubes, nanorods or nanospheres.
  • About 0.34 g of the silver nitrate is dissolved in 10 ml of deionised water to form a mixture.
  • the mixture is then added to a container containing about 4 g of the nanotubes, nanorods or nanospheres to form a matrix. Removing excess solvent from the matrix
  • excess water is removed by drying the matrix at room temperature for 24 hours and subsequently in an oven at 120 degrees Celsius for 24 hours. It was observed that the concentration of the loaded silver nitrate differs due to the nature of the ⁇ 2 form used. In all instances, nitrate is used as a precursor, and water is used as a solvent due to excellent solubility of the nitrate in water.
  • the matrix is calcined at 300 degrees Celsius for 12 hours to remove the nitrate moiety from the silver nitrate to form a composite matrix (nanotubular, nanorod, or nanospherical).
  • each one of the three prepared composite matrix is incubated with a growing culture of E. coli K- 12 strain in order to establish if the matrices could reduce the growth of E. coli within a short period of time when Ti0 2 is exposed to sunlight ( Figures 1 , 2, and 3).
  • the nanorod and nanospherical composite matrices were able to reduce the growth of E. coli, but showing insignificant levels of growth reduction ( Figures 1 and 2). It was surprisingly found that the reduction of E. coli is attributed to the form of the composite matrix.
  • the nanotubular composite matrix was found to have the largest surface area and thus being more effective in reducing the growth of E. coli when compared with the nanorod and nanospherical composite matrices. Although this specific example pertains to E. coli, the matrix has been found to be highly effective against a broad spectrum of undesirable microorganisms and contaminants.
  • a device for reducing contaminants in water, the device comprising a container, with the nanotubu!ar composite matrix as (described above) being disposed within the container.
  • the device is made available to communities in remote areas where there are limited resources to reduce contaminants in water.
  • the contaminated water is disposed in the container and incubated whilst in contact with the nanotubular composite matrix in the container for 15 minutes thus to reduce the contaminants in the water.
  • the nanotubular composite matrix could be an effective way to improve water quality and reduce diarrheal disease from waterborne, bacterial and viral pathogens.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
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Abstract

This invention relates to a method for preparing a nanotubular composite matrix for reducing contaminants in water and on the matrix's surface including the steps of preparing a photocatalytic agent in nanotubular form; dissolving an antimicrobial agent in a solvent; impregnating the photocatalytic agent with the antimicrobial agent in solution to form a matrix; removing excess solvent from the matrix; and calcining the matrix to remove a moiety of the antimicrobial agent to form the nanotubular composite matrix. The invention further relates to a method for reducing contaminants in water including the steps of providing a nanotubular composite matrix; incubating the water in the matrix; and activating the photocatalytic agent by exposing the matrix to a light source. The applicant has found that the method according to the invention reduces contaminants in water within 15 minutes in the presence of sunlight.

Description

METHOD FOR REDUCING CONTAMINANTS IN WATER
INTRODUCTION AND BACKGROUND TO THE INVENTION The present invention relates to a method and matrix for reducing contaminants in water and to a method for preparing such a matrix.
Owing to poverty and scarcity of resources, contaminated water containing unacceptable levels of toxic substances and pathogens is often used by humans for consumption, agricultural irrigation, or recreation. The use of such contaminated water leads to infection and development of disease. The World Health Organization (WHO) recommends that any water intended for drinking should contain zero total faecal coliform counts in any 100 ml sample.
Currently, a number of methods are used for purifying water, including ultraviolet light, low frequency ultrasonic irradiation, distillation, reverse osmosis, water sediment filters, activated carbon, and ozonisation. A disadvantage of these methods is that they require relatively expensive apparatus, placing them outside of reach of most of the population exposed to contaminated water.
Furthermore, halogens such as chlorine (CI) and bromine (Br) are well known and widely used as antibacterial agents, but the direct use of these halogens as antibacterial agents has many disadvantages, because of their high toxicity and high vapour pressure in pure form. Another disadvantage associated with the use of halogens is that they may potentially react with other chemical contaminants to form by-products that could be carcinogenic.
Yet another disadvantage of these methods is that some of them, such as those using activated carbon, insufficiently remove contaminants (bacteria, algae and fungi) from water. In addition, they may require an extended period of time to sufficiently reduce the contaminants. Another disadvantage experienced with the above method is that they have limited efficiency whilst being costly and time consuming. US2712573 discloses a method for removing contaminants and pathogens from water comprising the steps of:
- placing an adsorbent (Ti02) in a container;
- pouring water through the adsorbent into the container;
- adsorbing at least a portion of the contaminants on the adsorbent; and
- irradiating the water with ultraviolet radiation,
wherein the adsorbent remains in contact with the water during the irradiation step. One of the disadvantages disclosed in US2712573 is that the method for water purification uses irradiation from an electric light bulb having a specific spectrum of 200 nm to 400 nm. In addition, U32712573 is limited only to the contaminated water exposed to such spectrum of ultraviolet radiation. A further disadvantage is that the method requires a reliable source of electricity and light, without any risk of interruption.
In addition, if the water quality is low or if the lamp sleeve surface is dirty, the intensity may be insufficient to completely inactivate the most UV- resistant microorganisms, such as adenoviruses.
US20100032353 discloses a liquid dispenser or water purification unit having a housing and a mouthpiece configured for contact with the mouth of a person. At least part of the mouthpiece is provided with an antimicrobial surface coating comprising silver nanoparticles complexed with titanium dioxide.
A disadvantage associated with US20100032353 is that the filter embedded in the unit lasts only a year, (approximately 700 liters) meaning users must replace the unit annually. A further disadvantage is that the antimicrobial surface is not used for water purification, but to ensure that bacteria from one person holding or drinking from the mouthpiece are killed on contact with the antimicrobial, such that a second person using the mouthpiece is not infected by the bacteria.
The above disadvantages have led to a need for alternative methods that are cost and time efficient, sustainable, robust, and posses low risk to humans and the environment.
OBJECTS OF THE INVENTION It is accordingly an object of the present invention to provide a method and matrix for reducing contaminants in water and on the matrix's surface and a method for preparing such a matrix with which the aforesaid disadvantages could be overcome or at least minimised. SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a nanotubular composite matrix for reducing contaminants in water comprising a photocatalytic agent in nanotubular form loaded with an antimicrobial agent.
Further according to the invention, the photocatalytic agent is a body of titanium dioxide (Ti02) nanotubes. The nanotubes may have a cross- sectional diameter of from 2 nm to 200 nm, preferably 7 nm to 1 1 nm.
Further according to the invention, the antimicrobial agent is a body of silver (Ag) particles. The particles may have a cross-sectional diameter of from 0.5 nm to 30 nm, preferably 1 nm to 5 nm.
According to a second aspect of the invention there is provided a method for preparing a nanotubular composite matrix for reducing contaminants in water and on the matrix's surface including the steps of:
- preparing a photocatalytic agent in nanotubular form;
- dissolving an antimicrobial agent in a solvent;
- loading the photocatalytic agent with the antimicrobial agent in solution to form a matrix;
- removing excess solvent from the matrix; and
- calcining the matrix to remove a moiety of the antimicrobial agent to form the nanotubular composite matrix.
The step of preparing the photocatalytic agent in the form of titanium dioxide may include the step of adding the titanium dioxide in an alkali salt to form a mixture, wherein the alkali salt may have a concentration of at least 2 M, preferably from 5 M to 30 M.
The titanium dioxide in the mixture may be selected in the range of from 2% to 50% (w/v), preferably from 10% to 30% (w/v).
The alkali salt may be selected from the group consisting of potassium hydroxide, sodium hydroxide, and calcium hydroxide.
The step of preparing the photocatalytic agent may include the further step of stirring the mixture at an elevated temperature of up to 300 degrees Celsius for up to 24 hours to form titanium dioxide nanotubes. Furthermore, the step of preparing the photocatalytic agent may include the further step of centrifuging the mixture to separate the nanotubes from the alkali salt.
Also, the step of preparing the photocatalytic agent may include the further step of washing the nanotubes with deionised water to remove excess alkali salt from the nanotubes and to maintain conductivity of the nanotubes constant below 100 pS/cm.
In addition, the step of preparing the photocatalytic agent may include the further step of drying the nanotubes at a temperature up to 200 degrees Celsius for at least 2 hours, preferably at 120 degrees Celsius for 12 hours and subsequently at 25 degrees Celsius for 5 hours. In addition, the step of preparing the photocatalytic agent may include the further step of sieving the nanotubes having an external diameter of from 2 nm to 200 nm, preferably from 7 nm to 1 1 nm, in accordance with the first aspect of the invention.
Further according to the invention, the step of dissolving the antimicrobial agent in the solvent may include the step of selecting the solvent from the group consisting of organic solvents and inorganic solvents, preferably inorganic solvents, further preferably deionised water.
Further according to the invention, the step of dissolving the antimicrobial agent in the solvent may further include the antimicrobial agent having a concentration in the range of from 0.1 % to 15% (w/v), preferably 0.5% to 7% (w/v).
The step of loading the photocatalytic agent with the antimicrobial agent may include the step of mixing the dried nanotubes with the antimicrobial agent in solution to form the matrix. The step of removing the excess solvent from the matrix may include the step of incubating the matrix at a temperature up to 250 degrees Celsius for at least 10 hours, preferably at 25 degrees Celsius for 24 hours and subsequently at 120 degrees Celsius for 24 hours. The step of calcining the matrix to remove the moiety of the antimicrobial agent may include the step of elevating the temperature up to 1000 degrees Celsius for at least 5 hours, preferably 300 degrees Celsius for 12 hours to form the nanotubular composite matrix of the first aspect of the invention.
Further according to the invention, the moiety of the antimicrobial agent is nitrate (N03).
According to a third aspect of the invention there is provided a method for reducing contaminants in water including the steps of:
- providing a nanotubular composite matrix according to the first aspect of the invention and/or prepared in accordance with the second aspect of the invention;
- incubating the water in the matrix; and
- activating the photocatalytic agent by exposing the matrix to a light source. Further according to the invention, the light source may be selected from the group consisting light buib or sunlight, preferably sunlight.
According to a fourth aspect of the invention there is provided a device for reducing contaminants in water, the device comprising:
a container; and
- a nanotubular composite matrix according to the first aspect of the invention disposed within the container.
Further according to the invention, the container is of a translucent material to allow light to pass through the container to activate a photocatalytic agent. Alternatively, the container is provided with a light source.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described further, by way of example only, with reference to the accompanying drawings wherein:
Figure 1 is a graph depicting the fraction of survivors of Escherichia coli (£. coli) culture incubated with a nanospherical composite matrix at varying concentration when a photocatalytic agent is exposed to ultraviolet radiation from sunlight for 90 minutes; Figure 2 is a graph depicting the fraction of survivors of £. coli culture incubated with a nanorod composite matrix at varying concentration when a photocatalytic agent is exposed to ultraviolet radiation from sunlight for 90 minutes; and
Figure 3 is a graph depicting the fraction of survivors of E. coli culture incubated with a nanotubular composite matrix according to a preferred embodiment of the invention at varying concentration when a photocatalytic agent is exposed to ultraviolet radiation from sunlight for 90 minutes.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
A non-limiting example of a preferred embodiment of the invention described in more detail below.
High level description of invention
in accordance with a preferred embodiment of the present invention, a method for preparing a nanotubular composite matrix for reducing contaminants in water and on the matrix's surface includes the steps of:
- preparing a photocatalytic agent comprising titanium dioxide in nanotubular form to form titanium dioxide nanotubes: - dissolving an antimicrobial agent in the form of silver nitrate having a concentration of between 0.1 % to 15% (w/v), preferably 0.5% to 7% (w/v), further preferably 3.4% in an inorganic solvent, such as deionised water;
- loading the nanotubes with the silver nitrate in solution to form a matrix;
~ removing excess solvent from the matrix by incubating the matrix at a temperature of up to 250 degrees Celsius for at least 10 hours, preferably at 25 degrees Celsius for 24 hours and subsequently at 120 degrees Celsius for 24 hours; and
- calcining the matrix to remove a moiety in the form of nitrate (N03) of the silver nitrate (AgN03) at an elevated temperature of up to 1000 degrees Celsius for 5 hours, preferably 300 degrees Celsius for 12 hours, to form a nanotubular composite matrix.
The step of preparing the photocatalytic agent in the form of titanium dioxide includes the step of adding the titanium dioxide in an alkali salt to form a mixture, wherein the alkali salt may have a concentration of at least 2 M, preferably from 5 M to 30 M.
The step of preparing the photocatalytic agent includes the step of stirring the mixture at an elevated temperature of up to 300 degrees Celsius for at least 12 hours, preferably 150 degrees Celsius for 24 hours to form the titanium dioxide nanotubes.
Furthermore, the step of preparing the photocatalytic agent includes the further step of centrifuging the mixture to separate the nanotubes from the alkali salt.
Also, the step of preparing the photocatalytic agent includes the further step of washing the nanotubes with deionised water to remove excess alkali salt from the nanotubes and to maintain conductivity of the nanotubes constant below 100 pS/cm.
In addition, the step of preparing the photocatalytic agent includes the further step of drying the nanotubes at a temperature up to 200 degrees Celsius for at least 2 hours, preferably at 120 degrees Celsius for 12 hours and subsequently at 25 degrees Celsius for 5 hours.
In addition, the step of preparing the photocatalytic agent includes the further step of sieving the nanotubes. The nanotubes have a cross- sectional diameter of from 2 nm to 200 nm, preferably 7 nm to 1 1 nm.
Detailed description of respective steps in the method according to the invention: Preparing Ti02 nanotubes, nanorods or nanospheres
The first step of the method, according to a preferred embodiment of the invention, is to prepare the titanium dioxide in a nanotubular form. Furthermore, other forms of the titanium dioxide, such as nanorod and nanospherical, were also prepared from a commercial P25 Degussa titania to establish which form of titanium dioxide is capable of reducing contaminants in water. In order to prepare the titanium dioxide nanotubes, about 23 g of the Degussa titania powder is placed in a teflon container together with 150 ml of 18 M potassium hydroxide to form a mixture. The mixture is stirred at a constant rate of 500 rpm in an autoclave at a temperature of 150 degrees Celsius for 24 hours. Alternatively, the mixture is stirred at a constant rate of 500 rpm in a microwave reactor for 5-10 minutes. The mixture is allowed to cool at room temperature for 24 hours to form titanium dioxide nanotubes. Subsequently, the nanotubes are separated from the mixture by centrifugation at a stirring rate of 10 000 rpm for 30 minutes at 4 degrees Celsius. The nanotubes are again washed with deionised water to remove excess potassium hydroxide from the nanotubes and to maintain conductivity of the nanotubes constant below 100 pS/cm. It was noted that removal of the alkali salt from the nanotubes could take at least a week. The nanotubes are dried in an oven at 120 degrees Celsius for 12 hours and then allowed to cool to room temperature for 5 hours. The nanotubes are then sieved to a desired size. The nanotubes have a cross-sectional diameter of from 7 nm to 1 1 nm. The above method is also followed when preparing the titanium dioxide in a nanorods form but 10 M of potassium hydroxide is used instead.
Further according to the invention, the titanium dioxide in a nanospherical form is prepared by using the above commercial P25 Degussa titania powder. Firstly, the powder is modified and then used. The modification is achieved by mixing the powder with water and then compressed into a moist paste. This moist paste is then dried in an oven at 120 degrees Celsius for 48 hours to form the titanium dioxide nanospheres. The nanospheres are cooled and crushed into fragments. The fragments having the desired size of the nanospherical form are sieved out. The larger fragments are recycled and re-sieved while the smaller ones (fine powder formed as a result of crushing) are mixed with water again to from the moist paste.
Loading Ti02 nanotubes, nanorods or nanospheres with Ag
According to a further step of the invention the silver nitrate is prepared and loaded to the nanotubes, nanorods or nanospheres. About 0.34 g of the silver nitrate is dissolved in 10 ml of deionised water to form a mixture. The mixture is then added to a container containing about 4 g of the nanotubes, nanorods or nanospheres to form a matrix. Removing excess solvent from the matrix
According to a further step of the invention, excess water is removed by drying the matrix at room temperature for 24 hours and subsequently in an oven at 120 degrees Celsius for 24 hours. It was observed that the concentration of the loaded silver nitrate differs due to the nature of the ΤΊΟ2 form used. In all instances, nitrate is used as a precursor, and water is used as a solvent due to excellent solubility of the nitrate in water. The matrix is calcined at 300 degrees Celsius for 12 hours to remove the nitrate moiety from the silver nitrate to form a composite matrix (nanotubular, nanorod, or nanospherical).
Reducing contaminants in water using the matrix
Further according to a preferred embodiment of the invention the composite matrix is used in a method for reducing contaminants in water that includes the steps of:
providing a nanotubular composite matrix prepared in accordance with the above preferred embodiment of the invention;
- incubating the water in the matrix; and - activating the photocatalytic agent in the form of titanium dioxide by exposing the matrix to a Sight source in the form of suniight.
According to a further step of the invention, each one of the three prepared composite matrix is incubated with a growing culture of E. coli K- 12 strain in order to establish if the matrices could reduce the growth of E. coli within a short period of time when Ti02 is exposed to sunlight (Figures 1 , 2, and 3). The applicants surprisingly found that the nanotubular composite matrix is effective in reducing the growth of E. coli when incubated with a growing culture for a minimum of 15 minutes (Figure 3). The nanorod and nanospherical composite matrices were able to reduce the growth of E. coli, but showing insignificant levels of growth reduction (Figures 1 and 2). It was surprisingly found that the reduction of E. coli is attributed to the form of the composite matrix. Furthermore, the nanotubular composite matrix was found to have the largest surface area and thus being more effective in reducing the growth of E. coli when compared with the nanorod and nanospherical composite matrices. Although this specific example pertains to E. coli, the matrix has been found to be highly effective against a broad spectrum of undesirable microorganisms and contaminants.
Further according to the invention, there is provided a device (not shown) for reducing contaminants in water, the device comprising a container, with the nanotubu!ar composite matrix as (described above) being disposed within the container. The device is made available to communities in remote areas where there are limited resources to reduce contaminants in water. In use, the contaminated water is disposed in the container and incubated whilst in contact with the nanotubular composite matrix in the container for 15 minutes thus to reduce the contaminants in the water. The advantages of the current device over the known prior art devices are that the current device is straightforward and uncomplicated to use and it does not require any electricity as it reduces contaminants in water within 15 minutes in the presence of sunlight. The applicants foresee a cost effective and environmentally acceptable nanotubular composite matrix to be used in reducing water contaminants, such a metal ions, organic solutes and microorganisms when the titanium oxide is exposed to sunlight. Furthermore the applicant anticipates that the nanotubular composite matrix would contribute towards solving water purification challenges post by prior art methods and apparatus by providing a method that is cost and time efficient (less than 20 minutes), sustainable, robust, and posses low risk to humans and the environment.
In addition, it is foreseen that the nanotubular composite matrix could be an effective way to improve water quality and reduce diarrheal disease from waterborne, bacterial and viral pathogens.
It will be appreciated that variations in detail are possible with a method and matrix for reducing contaminants in water and to a method for preparing such a matrix according to the invention without departing from the scope of the appended claims.

Claims

1 . A nanotubuiar composite matrix for reducing contaminants in water comprising a photocatalytic agent in nanotubuiar form loaded with an antimicrobial agent.
2. A nanotubuiar composite matrix according to claim 1 wherein the photocatalytic agent is a body of titanium dioxide (Ti02) nanotubes.
3. A nanotubuiar composite matrix according to claim 2 wherein the nanotubes have a cross-sectional diameter of from 2 nm to 200 nm, preferably 7 nm to 1 1 nm.
4. A nanotubuiar composite matrix according to any one of claims 1 to 3 wherein the antimicrobial agent is a body of silver (Ag) particles.
5. A nanotubuiar composite matrix according to claim 4 wherein the particles have a cross-sectional diameter of from 0.5 nm to 30 nm, preferably 1 nm to 5 nm.
6. A method for preparing a nanotubuiar composite matrix for reducing contaminants in water and on the matrix's surface including the steps of:
- preparing a photoeatalytic agent in nanotubular form;
- dissolving an antimicrobial agent in a solvent;
- loading the photoeatalytic agent with the antimicrobial agent in solution to form a matrix;
- removing excess solvent from the matrix; and
- calcining the matrix to remove a moiety of the antimicrobial agent to form the nanotubular composite matrix.
A method for preparing a nanotubular composite matrix according to claim 6 wherein the step of preparing the photoeatalytic agent in the form of titanium dioxide includes the step of adding the titanium dioxide in an alkali salt to form a mixture, wherein the alkali salt has a concentration of at least 2 M, preferably from 5 M to 30 M.
8. A method for preparing a nanotubular composite matrix according to claim 7 wherein the titanium dioxide in the mixture is selected in the range of from 2% to 50% (w/v), preferably from 10% to 30% (w/v).
9. A method for preparing a nanotubular composite matrix according to claim 7 or 8 wherein the alkali salt is selected from the group consisting of potassium hydroxide, sodium hydroxide, and calcium hydroxide.
10. A method for preparing a nanotubular composite matrix according to any one of claims 6 to 9 wherein the step of preparing the photocatalytic agent includes the further step of stirring the mixture at an elevated temperature of up to 300 degrees Celsius for up to 24 hours to form titanium dioxide nanotubes.
1 1 . A method for preparing a nanotubular composite matrix according to claim 10 wherein the step of preparing the photocatalytic agent includes the further step of centrifuging the mixture to separate the nanotubes from the alkali salt.
12. A method for preparing a nanotubular composite matrix according to claim 1 1 wherein the step of preparing the photocatalytic agent includes the further step of washing the nanotubes with deionised water to remove excess alkali salt from the nanotubes and to maintain conductivity of the nanotubes constant below 100 pS/cm.
13. A method for preparing a nanotubular composite matrix according to claim 12 wherein the step of preparing the photocatalytic agent includes the further step of drying the nanotubes at a temperature up to 200 degrees Celsius for at least 2 hours, preferably at 120 degrees Celsius for 12 hours and subsequently at 25 degrees Ceisius for 5 hours.
14. A method for preparing a nanotubular composite matrix according to claim 13 wherein the step of preparing the photocatalytic agent includes the further step of sieving the nanotubes having an external diameter of from 2 nm to 200 nm, preferably from 7 nm to 1 1 nm.
15. A method for preparing a nanotubular composite matrix according to any one of claims 6 to 14 wherein the step of dissolving the antimicrobial agent in the solvent includes the step of selecting the solvent from the group consisting of organic solvents and inorganic solvents, preferably inorganic solvents, further preferably deionised water.
16. A method for preparing a nanotubular composite matrix according to claim 1 5 wherein the antimicrobial agent has a concentration in the range of from 0.1 % to 15% (w/v), preferably 0.5% to 7% (w/v).
17. A method for preparing a nanotubular composite matrix according to claim 1 5 or 16 wherein the step of loading the photocatalytic agent with the antimicrobial agent includes the step of mixing the dried nanotubes with the antimicrobial agent in solution to form the matrix.
, A method for preparing a nanotubular composite matrix according to any one of claims 15 to 17 wherein the moiety of the antimicrobial agent is nitrate (N03).
A method according to any one of claims 6 to 18 wherein the step of removing the excess solvent from the matrix includes the step of incubating the matrix at a temperature up to 250 degrees Celsius for at least 10 hours, preferably at 25 degrees Celsius for 24 hours and subsequently at 120 degrees Celsius for 24 hours.
A method for preparing a nanotubular composite matrix according to any one of claims 6 to 19 wherein the step of calcining the matrix to remove the moiety of the antimicrobial agent includes the step of elevating the temperature up to 1000 degrees Celsius for at least 5 hours, preferably 300 degrees Celsius for 12 hours to form the nanotubular composite matrix of the first aspect of the invention.
A method for reducing contaminants in water including the steps of:
- providing a nanotubular composite matrix according to any one of claims 1 to 5 and/or prepared in accordance with the method according to any one of claims 6 to 20;
- incubating the water in the matrix; and - activating the photocatalytic agent by exposing the matrix to a light source
22. A device for reducing contaminants in water, the device comprising a container; and a nanotubular composite matrix according to any one of claims 1 to 5 of the invention disposed within the container.
23. A device for reducing contaminants in water according to claim 22 wherein the container is of a translucent material to allow light to pass through the container to activate a photocatalytic agent.
24. A device for reducing contaminants in water according to claim 22 wherein the container is provided with a light source.
25. A nanotubular composite matrix for reducing contaminants in water substantially as herein described and exemplified.
26. A method for preparing a nanotubular composite matrix for reducing contaminants in water substantially as herein described and exemplified.
27. A method for reducing contaminants in water substantially as herein described and exemplified. A device for reducing contaminants in water substantially as herein described and exemplified.
PCT/IB2012/057487 2011-12-22 2012-12-19 Method of reducing contaminants in water WO2013093805A1 (en)

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