Patent Application
20080020927
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:
a) and 1(b) illustrate the structure of the preferred embodiment of a metal-supporting photocatalyst according to this invention;
a) to 3(d) are scanning electron microscopy photographs to illustrate the relationship between the dispersion of nano-particles of titanium dioxide and the pH value of the aqueous solution containing silver deposit;
The metal-supporting photocatalyst according to this invention includes a metal deposit, and nano-particles of a photocatalyst dispersed on the metal deposit. The term “metal deposit” described hereinafter is a metallic material formed through a deposition process. In one preferred embodiment, the metal deposit is a metal electro-deposit, i.e., a deposit formed through an electrolytic process. More preferably, the metal deposit has a dendritic structure. Referring to
In addition, the branches 103 of the metal deposit may be made from one of a noble metal selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), and palladium (Pd), and a transition metal selected from the group consisting of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and zinc (Zn). Preferably, each of the branches 103 is made from an antibacterial metal selected from the group consisting of zinc (Zn), silver (Ag), and copper (Cu).
The nano-particles 101 of the photocatalyst are made from a photo-catalytical compound selected from the group consisting of titanium dioxide and zinc oxide. Preferably, more than 50% of the nano-particles of the photocatalyst are made from anatase titanium dioxide. Most preferably, more than 80% of the nano-particles of the photocatalyst are made from anatase titanium dioxide. Additionally, the nano-particles of the photocatalyst preferably have a size ranging from 5 nm to 100 nm. More preferably, the nano-particles of the photocatalyst have a size ranging from 5 nm to 20 nm.
According to this invention, when the branches 103 are made from an antibacterial metal selected from the group mentioned above, the metal-supporting photocatalyst of this invention is capable of performing antibacterial and environment-cleaning activities by the photocatalytic property of the nano-particles 101 of the photocatalyst in the presence of light irradiation, or by the antibacterial nature of the metal deposit in the absence of light irradiation.
In addition, it is known that the larger the specific surface area, the easier the photocatalyst could be coated on a carrier or base. Since the metal deposit of the metal-supporting photocatalyst according to this invention has a dendritic structure, which exhibits a relatively high specific surface area, e.g., more than 1.27 m2/g, the metal-supporting photocatalyst according to this invention can be directly coated or fixed on the carrier or base without the use of binders.
Referring to
The preferred embodiment of a method for preparing a metal-supporting photocatalyst according to this invention includes forming a metal deposit of a supporting metal, and forming nano-particles of a photocatalyst on the metal deposit. Preferably, the metal deposit thus formed has a dendritic structure. Preferably, formation of the metal deposit is conducted by electrolysis of a metal salt of the supporting metal through redox reaction in a low temperature solution or redox reaction aided with pulsed discharge plasma. Specifically, the metal deposit of a supporting metal is made by placing a metal electrode, which has an oxidation potential higher than that of the supporting metal, in an aqueous solution containing the metal salt of the supporting metal with application of pulsed discharge plasma so as to form the metal deposit of the supporting metal on the surface of the metal electrode.
Preferably, the supporting metal is selected from the group consisting of a noble metal selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), and palladium (Pd), and a transition metal selected from the group consisting of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and zinc (Zn). The metal salt is selected from the group consisting of nitrate, acetate, oxalate, carbonate, and sulfate of the supporting metal. More preferably, the supporting metal is an antibacterial metal selected from the group consisting of zinc (Zn), silver (Ag), and copper (Cu), and the metal salt is selected from the group consisting of nitrate, acetate, oxalate, carbonate, and sulfate of zinc (Zn), silver (Ag), or copper (Cu). Most preferably, the metal salt is silver nitrate.
In addition, the metal salt concentration of the aqueous solution, and temperature and pH value of the aqueous solution can be varied to achieve a desired structure of the metal deposit thus made, especially formation of the metal deposit having the dendritic structure. For example, the specific surface area will be decreased with the increase in pH value of the aqueous solution. Preferably, the aqueous solution contains nitric acid and ammonia, and has a pH value ranging from 2 to 4. Preferably, the metal salt concentration of the aqueous solution ranges from 1 wt % to 3 wt % based on the total weight of the aqueous solution.
The nano-particles of the photocatalyst may be dispersed on the metal deposit through dip-coating process or sol-gel process. Preferably, the dispersion of the nano-particles of the photocatalyst on the metal deposit can be controlled through pH adjustment of the aqueous solution in which the metal deposit is formed, and the concentration of the nano-particles of the photocatalyst in the aqueous solution. Preferably, the dispersion of the nano-particles of the photocatalyst on the metal deposit is conducted in the aqueous solution having pH value ranging from 11 to 12.
1. Preparation of a Metal Deposit Having a Dendritic Structure
Aqueous solutions of 1 wt %, 2 wt %, and 3 wt % of silver nitrate (AgNO3) (available from Mallinckrodt Co., tradename: MA-2169-01, CAS No.: 7761-88-8) were prepared. Then, copper (Cu) (available from J. T. Baker Co., tradename: JT-1728-01, CAS No.: 7440-50-8) was added in a molar ratio of AgNO3 to Cu equated to 2:1 into each of the aqueous solutions, i.e., 0.19 wt %, 0.38 wt % and 0.57 wt % of Cu were separately added into the solutions of 1 wt %, 2 wt %, and 3 wt % of silver nitrate (AgNO3). Next, nitric acid (available from J. T. Baker, tradename: JT-9601-01, CAS No.: 7697-37-2) andammonia solution (available fromTEDIA, tradename: AR-0147, CAS No.: 1336-21-6) were added into the aqueous solution in an amount sufficient to adjust the pH value of the aqueous solution to a range of from 3 to 9. Silver deposit was formed in each of the aqueous solutions due to oxidation potential difference between silver and copper. The specific surface area (BET surface) of the silver deposit respectively formed in the aqueous solutions of 1 wt %, 2 wt %, and 3 wt % of silver nitrate is shown in
2. Dispersion of Nano-Particles of Photocatalyst on the Silver Deposit
Nano-particles of titanium dioxide (available from Ishihara Sangyo Kaisha LTD., tradename: STS 21), in an amount of 1 wt %, 3 wt %, and 5 wt %, were separately added to the silver deposit formed in the aqueous solution of 3 wt % silver nitrate as mentioned above. Next, nitric acid (available from J. T. Baker, tradename: JT-9601-01, CAS No.: 7697-37-2) and ammonia solution (available from TEDIA, tradename: AR-0147, CAS No.: 1336-21-6) were added into the separate aqueous solutions so as to adjust the pH value to a range of from 3 to 12. The nano-particles of the titanium dioxide were dispersed on and were adhered to the silver deposit due to surface electrical difference therebetween. The metal-supporting photocatalysts with nano-particles of 1 wt %, 3 wt %, and 5 wt % of the titanium dioxide respectively dispersed on the silver deposit were made. It is noted that thea mount of nano-particles of the titanium dioxide should not exceed 5 wt % so as to prevent aggregation of the titanium dioxide particles on the silver deposit. The dispersion effect of the nano-particles of 5 wt % of titanium dioxide on the silver deposit for the aqueous solutions respectively having pH values of 4.5, 7.5, and 11 are shown in
3. Photocatalytic Effect of the Metal-Supporting Photocatalyst of This Invention
Each of the silver-supporting titanium dioxide photocatalysts obtained above, with nano-particles of 1 wt %, 3 wt %, and 5 wt % of the titanium dioxide dispersed on the silver deposit, were separately added into 100 ml of 0.01 wt % of methyleneblue solution in an amount of 1.5 g so as to form a test mixture. In addition, 100 ml of 0.01 wt % of methyleneblue solution without addition of the metal-supporting photocatalysts, and a mixture of 100 ml of 0.01 wt % of methyleneblue solution and the silver deposit were used as control groups 1 and 2. Each of the test mixtures and the control group 2 were irradiated with ultraviolet light having a wavelength of 235 nm for 20 minutes. The absorption strength under light wavelength ranging from 220 nm to 820 nm for each irradiated test mixture and control group 2, and the non-irradiated control group 1 is shown in
(A−A′)/A×100%,
where A stands for the integral area of the absorption peak of the curve for the origin (i.e., the control group 1) in
The decomposition efficiency results of each of the test mixtures and the control group 2 are shown in
4. Evaluation of Bactericidal Effect of the Metal-Supporting Photocatalyst of this Invention
Bactericidal effect of the metal-supporting photocatalyst of this invention against bacteria including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Methicillin resistant Staphylococcus aureus, and Escherichia coli 0157 was evaluated in accordance with Japan JISZ 2801:2000 standard. The results are shown in the following Table I.
Staphylococcus aureus
Escherichia coli
Pseudomonas aeruginosa
Staphylococcus aureus
Escherichia coli 0157
According to this invention, since the metal-supporting photocatalyst includes nano-particles of the photocatalyst evenly dispersed on a metal deposit, particularly a metal deposit with a dendritic structure, aggregation of the photocatalyst on the metal deposit can be avoided, and the photocatalytic activity of the nano-particles of the photocatalyst can be considerably enhanced.
In addition, since dispersion of the nano-particles of the photocatalyst on a metal deposit is achieved through surface electrical difference therebetween, addition of the binder or the anion or cation surfactants for fixing the photocatalyst particles to a carrier is unnecessary. Hence, the method of preparing the metal-supporting photocatalyst of this invention is relatively simple and cost effective.
Moreover, since the metal deposit included in the metal-supporting photocatalsyt according to this invention has a relatively low melting point, the metal-supporting photocatalsyt can be fixed to carriers or bases in a relatively low temperature environment, and phase transformation of the photocatalyst or the metal deposit due to thermal effect can be avoided.
Additionally, when the metal deposit is made from an antibacterial metal, the metal-supporting photocatalyst is capable of performing antibacterial and environment-cleaning activities in either a bright or dark environment.
While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.
