|Title of Invention||
"A PROCESS FOR THE PREPARATION OF SILVER DEPOSITED ACTIVATED CARBON"
|Abstract||A process for the preparation of silver deposited activated carbon catalyst using low voltage current by application of low voltage d.c. current in the range of 5-100 volts through silver wires or plates immersed in water containing purified active carbon under stirring for a period till the deposition of silver on active carbon in the range of 1 to 10%, evaporating water to dryness to get silver deposited activated carbon.|
|Full Text||The present invention relates to a process for the preparation of silver deposited activated carbon catalyst using low voltage current useful in controlling microorganism in water.
Application of low voltage d.c. current through silver wires or plates immersed in water yield smaller particles of metallic silver or its ions. These silver particles can kill bacteria and viruses present in water.
The present invention relates to a process wherein the silver particles produced by application of low voltage current on silver wires are in-situ deposited on activated carbon, which are useful in controlling the microorganism present in water. The microorganism present in water are mainly bacteria or viruses.
Most of the diseases are caused due to air and water pollution in the environment. Majority of the water-born diseases are spreading because of the poor quality of water, particularly due to the presence of bacteria and viruses in water. Hence it is utmost important to purify water before its use. There are several methods of water purification like chlorination, iodation, ozonation, UV-purification, reverse osmosis and more recently by using silver catalysts.
It is widely known that chlorine can be effectively used to deactivate bacteria present in water. Chlorine is commonly used for treating drinking water, and also for treating water used in swimming pools, and also used to treat waste water during sewage treatment processes. Even though, chlorination is known to be an effective method of killing bacteria in water, it has its own disadvantages, Chlorine which is relatively volatile gas in natural state, is quickly dissipated from water which is left to stand open to the atmosphere, particularly when the water has a temperature of greater than 70°F. Hence, it is necessary to add chlorine to water frequently in order to maintain the bacteria levels in the safe ranges and this has disadvantages from practical and economical points of view. Also water containing high levels of chlorine can be harmful to the eyes, skin and hair. Other methods like UV-purification and reverse osmosis are not cost effective.
Ever since silver has been recognized as an anti-bactericide, its application in purification of water is increasing. It has been reported that the use of silver may be linked to man's earliest attempts to improve his environment. Silver vessels have been used since ancient times to keep water, wine and vinegar pure and antibacterial action of silver is due to the fact that metallic silver is said to dissolve in water in about 10-5 g/l which is toxic to E.Coli and Bacillus typhosus, both of which can cause
virulent diseases. 2500- year long history of the use of silver for water purification and disease control has been established with no reports of toxic reactions to the hundreds of millions of children and adults exposed to it.
The ability of silver in water purification and disease control is reported (R.L. Davies and S.F. Etris, Catal. Today, 1997, 36, 107). It was not until 1986 that USA Patent No. 4,608,247 was issued to cover the catalytic action of silver in an aqueous media for the sanitation of water. Atomic oxygen adsorbed on the surface of the silver instantaneously oxidizes organic material on contact. The use of silver vessels to keep liquids pure for longer times has been known since ancient times. Cyrus the Great, King of Persia (550 - 529 B.C.), who established a board of health and a medical dispensary for his citizens, had water drawn from a designated stream then 'boiled and very many four wheeled wagons drawn by mules carry in silver vessels,'
following the king whithersoever he goes at any time (Herodotus, Book 1, Para. 188, translated by A.D. Godley, Harvard University Press, Cambridge, 1946). Pliny the Elder, in his great work, Natural History, (78 A.D.) reports in Book XXXIII Section XXXV, that the slag of silver has healing properties as an ingredient in plaster being extremely effective in causing wounds close up ...( Pliny the Elder, Natural History, Libri XXXIII, Part XXXV translated by Rackham, Volume IX, Hrvard University Press, Cambridge, 1952). In 1884, F. Crede, observing a relationship between 20% and 79% of children in various institutions of the blind and the presence of maternal and venereal disease, introduced the silver nitrate solution prophylxis for the eyes of newborns Following its introduction, the incidence of gonococcal ophthamia neonatorus dropped to about 0.2%. His prophylaxis became a state regulation in most countries throughout the world (Vivian Wahlberg, Acta Paediatrica Scandanavica, Supplement 295, Stockholm, 1982). Thus a 2500-year history of the use of silver for water purification and disease control has been established with no reports of toxic reactions to the hundreds of millions of children and adults exposed to it. In fact, the catalytic cartridge (C.F. Heining, US Patent No. 4,608247, August 26, 1986) containing silver micro crystals on a - A^C^ with a
copper sheath surrounding it has a capability of Ag and Cu to leach into the swimming pool by galvanic action without the application of electric current (C.F. Heining, Jr., Ozone Science and Engineering, 1993, p.533). It has been shown that silver thiosulfate incorporated in a complex encapsulated in silica gel microspheres
has positive bactericidal action against a variety of disease-causing bacteria such as E.coli and S.aureus as well as HIV-1103 (H. Oka, T. Tomioka, S. Ueda et al., Metal - Based Drugs, 1994, 1, 511). It was also reported that the silver salt of sulfadiazine has proved to be a most efficacious topical compound for reducing the development of early burn-wound sepsis (C.L. Fox, B.W. Rappole and W. Stanford, Surgery, Gynecology and Obstetrics, 1969, 128, 1021). Metallic silver is said to dissolve in water in about 10 ~5 g / 1 which is toxic to E.coli and Bacillus typhousus, both of which can cause virulent diseases (G.V. James, Water treatment, 4th ed., CRC Press, Cleveland, OH, 1971, p.38). Marketed by Katadyn Products, Inc., Switzerland, for over 50 years, the Katadyn filter uses 0.28% by weight of metallic silver in a ceramic fired to provide a pore diameter of 0.2 micrometres ((E. Habenschaden, Sterilization of water with Katadyn ceramic filters, Sonderdruck aus Pharma International, 1988 ).
Detailed Description of the Invention
Micro crystals of silver have a tendency to lightly bound nascent oxygen (with a binding energy of only 40 kcal/mol) and these species readily oxidizes bacteria or viruses, resulting in complete disintegration.
Only recently, it is known that silver may react with microorganism by any or all three of the following mechanisms :
(1) Destruction of microorganisms by oxidation catalyzed by silver
(2) Disruption of electron transfer in bacteria by monovalent silver. Disruption
of electron transfer in bacteria by monovalent silver, and/or preventing the
unwinding of DNA in viruses with substitution of hydrogen ions by
monovalent silver, and
(3) Destruction of bacteria and viruses by bivalent and trivalent silver.
Among all the metals, silver is unique in its affinity towards oxygen. It was
reported that atomic oxygen had an almost perfect fit in the octahedral holes of gold, silver and copper. However, in gold the electron cloud of oxygen tends to be expelled by lattice oxygen of gold atoms and this block the movement through holes. Copper, on the other hand forms the oxide providing an impossible barrier. Silver offers so little repulsion to oxygen that only a small amount of thermal energy is required to readily move the atomic oxygen through the silver lattice. This secret of oxidative capability of silver has been disclosed in a German Patent No. 228,687 in 1998 in the conversion of methanol to produce formaldehyde and ethylene to ethylene oxide.
The atomic oxygen adsorbed on to the surface of silver exposed to aqueous media readily reacts with pairs of sulfhydril (-S-H-) groups on the surface of the bacteria or viruses by replacing the hydrogen atoms (as water) resulting in the coupling of the sulfur atoms to form -R-S-S-R- bond which completely blocks the respiration process and electron transfer. Monovalent silver ions have an affinity for sulfhydril groups exposed on bacteria or viruses.
D.C. current through a set silver anodes immersed in water produces metal ion particles in colloidal range (0.0001 microns in diameter). In a true colloid, silver particles, which are electrically charged are animated by what is known as Brownian movement and remain in suspension almost indefinitely. Colloidal particles scatter the light, and depending up on their size they exhibit different colors. In fact, a critical indicator of the quality colloidal silver in water is its color. As the size of each silver particle gets larger, the color of the solution ranges from yellow to brown to red to gray and black. The ideal form of colloidal silver in water is golden yellow color at 20 ppm of supreme fine particles of 0.999% pure silver having 0.0001 microns in diameter. However the color depends on the purity of silver metal and also the impurities present in water.
The most commonly method of making silver on activated carbon is the impregnation of silver salt on the support. The higher oxidation state of silver in this salt when reduced in hydrogen flow at relatively high temperatures to get metallic particles, there is every chance of agglomeration of metallic particles to give bigger crystallites. The present invention is thus has several advantages like avoiding pretreatment conditions which prevents the metal sintering, generation of silver smaller particles which possess higher intrinsic activity (activity per site) compared to the bigger particles of silver.
The present invention relates to a process wherein the in-situ deposition of silver particles on activated carbon do not require any pretreatment conditions like calcinations (heating in air at high temperatures or reduction at high temperatures).
Another object of the present invention is that silver metallic particles of smaller diameter are formed and these particles are in-situ deposited on activated carbon.
The object of the invention is that low voltage d.c current in the range of 5 to 100 volts preferably in the range of 10 to 70 volts, more preferably in the range of 20
to 50 volts is sufficient in order to in-situ deposit smaller silver particles on activated carbon.
Another object of the present invention is that the silver particles deposited in-situ on activated carbon can be used to control microorganism like bacteria and viruses present in water.
Another object of the present invention is that the amount of silver deposited on active carbon is in the range of 1-10 percent by weight, preferably, in the range of 1-8 percent by weight, more preferably in the range of 1-5 percent by weight.
Thus the present invention has advantages over conventional method like impregnation, particularly, in preventing agglomeration and generation of silver metallic particles of smaller diameter on carbon without any pretreatment conditions. It is a known fact that smaller particles of metal possess high intrinsic activity compared to that of bigger metal particles.
Accordingly, the present invention provides a process for the preparation of silver deposited activated carbon catalyst using low voltage current which comprises application of low voltage d.c. current in the range of 5-100 volts through silver wires or plates immersed in water containing purified active carbon under stirring for a period till the deposition of silver on active carbon in the range of 1 to 10%, evaporating water to dryness to get silver deposited activated carbon.
Another embodiment of the present invention is a process for making silver on activated carbon catalyst by in-situ deposition of silver metal and the material thus prepared is active in controlling microorganism in water.
Another embodiment of the present invention is a process for making silver on activated carbon by application of low voltage d.c. current.
Yet another embodiment of the present invention is a process wherein no pretreatment conditions like cancinations, reduction at high temperatures are required.
Another embodiment of the present invention is a process wherein the silver particles deposited on activated carbon are in smaller diameter.
Another embodiment of the present invention is a process wherein the silver particles deposited in-situ on activated carbon can be used to control microorganism like bacteria and viruses present in water.
Another embodiment of the present invention is a process wherein the amount of silver deposited on active carbon is in the range of 1 - 10 percent by weight, preferably, in the range of 1 - 8 percent by weight, more preferably in the range of 1-5 percent by weight.
Application of low voltage d.c. current generates smaller particles of silver metal. Since no pretreatment conditions are maintained the in-situ deposition of silver on activated carbon retains smaller particles of silver metal. It is a well known fact that smaller metallic particles possess high intrinsic activity (activity per site is called intrinsic activity) compared to bigger metallic particles.
The catalyst mentioned in this invention is prepared by using commercial high surface area (surface area measured by BET method is approximately 1000 m2 gram* ') activated carbon as a support material. The silver loading is maintained at 2 percent by weight with respect to activated carbon. Silver is deposited on activated carbon by the application of low voltage d.c. current.
Prior to the deposition of silver particles on to activated carbon, the support is purified by treating with hot concentrated HNOs, hot de-ionized water, hot ammonia solution, again hot de-ionized water in a sequential manner for several times in order to remove metallic and other impurities.
Readycult® Coliforms 50 supplied by M/S. E. Merck, Germany is used for the detection of total coliforms in the water. The composition of this reagent is as follows
Tryptose 0.25, sodium chloride 0.25, sorbitol 0.05, tryptophan 0.05, di-potassium hydrogen phosphate 0.135, potassium dihydrogen phosphate 0.1, laurylsulfate sodium salt 0.005, X-GAL 0.004, MUG 0.0025 and IPTG 0.005
The high nutritional quality of the peptones and the incorporated phosphate buffer guarantee rapid growth of coliforms whereas laurylsulfate largely inhibits the accompanying flora, especially the gram positive. By adding the chromogenic substrate X-GAL which is cleaved by coliforms and the fluorogenic substrate MUG which is highly specific for E-coli the simultaneous detection of total coliforms and E-coli is possible. The presence of total coliforms is indicated by a blue-green colour of the brath and E-coli by a blue fluorescence under UV-light.
The present invention is described with reference to the following examples that are explained by way of illustrations only and should not therefore be construed to limit the scope of the present work.
10 grams of purified dried active carbon has been immersed in 2 litre distilled water and silver nano-particles are generated by passing low but constant voltage electricity (40V) through the silver electrodes (0.4mm thickness and 10mm width and 100mm long plates) immersed in distilled water , maintaining a constant rapid stirring for a period of 10 hours. A D.C. regulated power supply has been used to generate silver nano particles. During the 10 hour operation, approximately the amount of silver particles deposited on activated carbon is 1 - 2 percent by weight with respect to the weight of the support. The water is evaporated to dryness on a hot plate with stirring and the resultant catalyst is dried in an air oven for 12 hours. This catalyst is termed as Ag CS / C.
To a 50 ml of raw water (containing coliforms) sample taken in clean beaker, Igram of Ag CS / C catalyst is added and kept for one hour with constant stirring. The catalyst particles are then separated by filtration and the water is collected into a sterile, transparent 100ml vessel with screw cap, and the granules of the Readycult coliforms reagent (supplied by E.Merck, Germany) is added by breaking the snap pack. The vessel is sealed and shaken to completely dissolve the granules, it is Incubated for about 24 hours at 31 OK. The brath remained slightly yellow (no colour change), it is an indication of absence of total coliforms. It is an idication that the total coliformrs are killed with the action of silver particles on the activated carbon in Ag CS / C catalyst.
We claim :
1. A process for the preparation of silver deposited activated carbon catalyst
using low voltage current which comprises application of low voltage d.c.
current in the range of 5-100 volts through silver wires or plates immersed in
water containing purified active carbon under stirring for a period till the
deposition of silver on active carbon in the range of 1 to 10%, evaporating
water to dryness to get silver deposited activated carbon.
2. A process as claimed in claim 1 wherein the d.c. current used is preferably in
the range of 10-70 volts.
3. A process as claimed in claims 1-2 wherein the amount of silver deposited on
active carbon is in the range of 1-10 percent by weight, preferably, in the
range of 1-8 percent by weight, more preferably in the range of 1-5 percent
4. A process for the preparation of silver deposited activated carbon
substantially as herein described with reference to the examples.
|Indian Patent Application Number||1055/DEL/2003|
|PG Journal Number||34/2008|
|Date of Filing||28-Aug-2003|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001, INDIA.|
|PCT International Classification Number||B01D 46/10|
|PCT International Application Number||N/A|
|PCT International Filing date|