1. Field of the Invention
The present invention relates generally to the membrane electrodes and to methods for sterilization of water, and particularly to a method of making a water-sterilizing polymeric membrane that can be used as a filter electrode for the sterilization of water through application of an electric field.
2. Description of the Related Art
The lack of potable water is a major problem in many areas of the world. A wide variety of sterilization and decontamination techniques exist for producing potable water. However, most are either difficult and/or costly to implement. The use of silver membrane filters for sterilization is of interest, primarily due to its portability, but the most effective form of silver for such purposes is nanostructures embedded in a matrix membrane. Most nano-production methods are difficult and costly to implement.
Additionally, silver alone is not optimally effective. Thus, the combination of silver nano-structures with other antimicrobial materials and techniques is of further interest. However, given that the nano-structure basis of the material is already difficult to manufacture, adding further materials and techniques compounds the difficulty in providing a cost-effective and efficient matrix membrane filter.
Thus, a method of making a water-sterilizing polymeric membrane solving the aforementioned problems is desired.
The method of making a water-sterilizing polymeric membrane relates generally to the manufacture of a polymeric matrix membrane for water sterilization, and to its use for the sterilization of water. The matrix membrane is made from cotton fiber coated with acid-doped conducting polyaniline and silver nanostructures. The silver nanostructures may be in the form of silver nanoparticles, silver nanowires, silver flakes, combinations thereof, and the like. The silver nanostructures may be prepared separately and then added to the polyaniline coated cotton fibers, or they may be synthesized in situ during the formation of the polyaniline (polymerization of aniline) coating on the cotton fibers. The latter process is a cost effective and relatively easy method for the preparation of the matrix membrane.
In use, the matrix membrane is used as a water filtration electrode by passing electrical current therethrough. Then, water to be sterilized is passed through the electrified matrix membrane, producing potable drinking water. The polyaniline, silver and electrical current all contribute to antimicrobial activity in the matrix membrane.
These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.
Similar reference characters denote corresponding features consistently throughout the attached drawings.
The method of making a water-sterilizing polymeric membrane begins by first coating cotton fiber with polyaniline doped with an acid, forming a first composite material. The first composite material is then coated with silver nano structures to form a second composite material. The second composite material, which is a composite of cotton fiber, polyaniline and silver, is then formed into a matrix membrane. The silver nanostructures may be in the form of silver nanoparticles, silver nanowires, silver flakes, combinations thereof, and the like. The coating of the first composite material with the silver nanostructures is performed with dip coating, conformal coating or any other suitable type of coating method. The polyaniline is doped with any suitable acid, such as hydrochloric acid, nitric acid, formic acid, phosphoric acid, sulfuric acid, acetic acid, methanesulfonic acid, trifluromethanesulfonic acid, p-toluenesulfonic acid, naphthalene sulfonic acid, dinonylnaphthalenesulfonic acid, camphorsulfonic acid, polystyrenesulfonic acid, dodecylbenzenesulfonic acid, or combinations thereof.
As illustrated in the reaction of
The reaction is preferably carried out at room temperature for a period of between one hour and sixty days. In experiments, aniline and silver nitrate solutions were prepared in 1 M nitric acid solution. The reactions were carried out in a 25 ml vial. In one reaction, 7.5 ml of 0.8 M aniline solution and 3 ml of 2.0 M silver nitrate solution were added to the vial and mixed by shaking. Then, a 150 mg cotton sample was placed inside the vial and the reaction was kept at room temperature without shaking. The progress of the reaction was monitored by both color and resistance changes of the cotton fibers sampled at different reaction intervals. After 21 days, the reaction was stopped and the resultant cotton/polyaniline/silver composite was removed from the reaction solution and washed several times with de-ionized water. The composite was then dried in air for 24 hours. The resistance of the cotton/polyaniline/silver composite was 30 Ω/sq.
Additionally, an auxiliary reducing agent (dimethyl formamide (DMF), formic acid, citric acid, ascorbic acid, formaldehyde, hydrogen peroxide, sucrose, and combinations thereof) may be added to increase the rate of the reaction. The auxiliary reducing agent preferably has a concentration of between 0.0001 M and 5.0 M. In experiments with the use of a reducing agent, aniline and silver nitrate solutions were prepared in 1 M nitric acid solution. The reactions were carried out in a 25 ml vial. In one reaction, 8 ml of 0.8 M aniline solution, 8 ml of 2.0 M silver nitrate solution and 4 ml DMF (as the auxiliary reducing agent) were added to the vial and mixed by shaking. Then, a 250 mg cotton sample was placed inside the vial, and the reaction was kept at room temperature without shaking. The progress of the reaction was monitored by both color and resistance changes of the cotton fibers sampled at different reaction intervals. After 12 days, the cotton/polyaniline/silver composite was removed from the reaction solution and washed several times with de-ionized water. The composite was then dried in air for 24 hours. The resistance of the cotton/polyaniline/silver composite was 2 Ω/sq.
The polyaniline doped with the acid, such as nitric acid, may be de-doped using any suitable base, such as ammonium hydroxide, and then re-doped with inorganic, organic or polymeric acids, such as hydrochloric acid, nitric acid, formic acid, phosphoric acid, sulfuric acid, acetic acid, methanesulfonic acid, trifluromethanesulfonic acid, p-toluenesulfonic acid, naphthalene sulfonic acid, dinonylnaphthalenesulfonic acid, camphorsulfonic acid, polystyrenesulfonic acid, dodecylbenzenesulfonic acid, and combinations thereof.
When using DMF as the reducing agent, the resultant composite material is found to consist of various silver nanostructures, including nanoribbons, nanowires, hexagonal flakes and triangular particles, and with polyaniline brushes that form on both the cotton fibers and on the silver nanostructures with coating thicknesses of between 50 nm and 200 nm. It should be understood that other types of fiber material, rather than only cotton, may be used, such as wool, glass wool, ceramic, inorganic or synthetic fibers, combinations thereof or combinations thereof with cotton fiber.
As shown in the reaction of
In the further alternative method of making the composite, illustrated in
In experiments utilizing the above alternative method, 0.40 g of cotton fibers were soaked for two hours in a 0° C. cooled solution of 1.05 g aniline dissolved in 40 ml of 1 M HCl in a 100 ml flask. Another solution of 2.6 g ammonium peroxydisulfate dissolved in 20 ml of 1 M HCl was prepared and cooled to 0° C. The oxidizing agent solution was added directly to the aniline solution with strong stirring, and the reaction temperature was maintained at 0° C. for four hours. Then, the reaction was left overnight at room temperature. The resultant green cotton/polyaniline composite was washed repeatedly with de-ionized water, 1 M HCl and finally with acetone. The composite was then dried at 50° C. under vacuum for two hours. The resistance of the cotton/polyaniline composite was 100 Ω/sq.
About 100 mg of the prepared cotton/polyaniline fibers was placed in 10 ml of 2.0 M silver nitrate solution/1 M nitric acid for a period of one week. The resultant cotton/polyaniline/silver composite was washed with de-ionized water, followed by rinsing with 0.5 M nitric acid. The composite was then dried at room temperature for 24 hours. The resistance of the composite was 20,000 Ω/sq.
In use, as shown in
In experiments, 80 mg of the matrix membrane was used as one electrode 12, and placed in a plastic funnel with a 5 mm diameter (in the lower, thinner portion of the funnel) and with a length of 3 cm. Contaminated water samples containing a nominal E. Coli bacterial density of 107-108 CFU/ml, were passed through the membrane filter with an adjusted rate of 15 ml/min. In each experimental run, a 100 ml water sample was allowed to flow through the device 10, and the treated solution was diluted 1,000 times, from which 100 μl was plated. The device 10 was operated with an applied voltage of 20 V. The bacterial inactivation efficiency was found to be 92% after the first run, and no E. Coli colonies were observed in the second run.
Overall, the sheet resistance of the matrix membrane prepared by any of the above methods is between 1 and 106 Ω/sq. The silver content varies between 5% and 85% by weight of total composition. The system 10 may be used for the removal of common bacterial contamination of water, such as E. Coli, S. aureus, P. vulgaris and P. aeruginosa. The applied voltage is preferably up to ±100 V. The flow speed of the water passing through the matrix membrane filter 12 may be between 10 and 10,000 ml/min., and the water may be passed therethrough any suitable number of times, with two or three runs being preferred.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.