Biophysical Properties of Silver (Ag+)

Silver has a number of unique properties including its strength, malleability and ductility, its electrical and thermal conductivity, its sensitivity to and high reflectance of light and the ability to endure extreme temperature ranges. Silver is an important catalyst in organic chemistry which may account in part for its activity against microbes. Silver nanoparticles of 1 -20 nm  remain unmetabolised in the human body, do not accumulate in tissues, are not affected by stomach hydrochloric acid and are rapidly excreted by the kidney and are completely nontoxic. Silver ions on the other hand can enter into chemical reactions, such as with Hydrochloric Acid in the stomach.  Go Chemless has researched novel high frequency technologies to ensure the smallest silver nanoparticles devoid of ions.

Abundance:
Silver occurs in the metallic state, commonly associated with gold, copper, lead, and zinc. It is also found in some 60 minerals including: argentite (a sulfide), cerargyrite (a chloride), many other sulfides and tellurides.

Atomic:

atomic diameter = twice the radius of 144 pm = 0.288 nanometres.

Nanoscience:

Nanoclusters have been called a new state of matter where the particles behave as separate entities not bound by the influence of, or attachment to, other atoms and molecules.  They also behave uniquely and anomalously to magnetic fields.  Nanoclusters are extremely stable, acts like a single atom and are predisposed to form with only certain number of atoms (magic numbers) especially 8, 20, 40, 58, 93.  They may also form a Bose-Einstein Condensate where all the atoms lose individuality and become superconductive with no losses or inefficiency. Although they are inherently neutral, they may take on a negative charge which further prevents interaction with other negatively charged entities such as Anions. When they are less than 10 nm, they easily pass through the blood-brain barrier and into the Mitochondria and are rapidly excreted through the kidney. They have powerful catalytic effects on organic molecules and on oxidation reactions such as used by bacteria and viruses.

Reactions:
Reacts mildly with the Oxygen in air: mild, =>Ag2O
No reaction with concentrated Hydrochloric Acid (HCl)
Reacts with strong Nitric Acid (AgNO3) to form Silver Nitrate

Magnetics:

Silver has only one loose electron (its magnetic moment remains without being cancelled by other electrons) in 5s shell, and this electron, if placed in a strong magnetic field, can split its spin either UP or DOWN.

Medical Applications:

While silver’s importance as a bactericide has been documented only since the late 1800s, its use in purification has been known throughout the ages. Early records indicate that the Phoenicians, for example, used silver vessels to keep water, wine and vinegar pure during their long voyages. In America, pioneers moving west put silver and copper coins in their water barrels to keep it clean. In fact, “born with a silver spoon in his mouth” is not a reference to wealth, but to health. In the early 18th century, babies who were fed with silver spoons were healthier than those fed with spoons made from other metals, and silver pacifiers found wide use in America because of their beneficial health effects. Silver also has a variety of uses in pharmaceuticals. In fact, silver sulfadiazine is the most powerful compound for burn treatment. It is used by every hospital in North America for burn victims to kill bacteria and allow the body to naturally restore the burn area. It is used world-wide. It is sold under the trade name of Silvadiene. In another application polyurethane central venus catheters impregnated with silver sulfadiazine and chlorhexidine to eliminate catheter-related bacteriemia are supplied by Arrow International, Reading, PA. In a world concerned with the spreading of virus and disease, silver is increasingly being tapped for its bactericidal properties and used in treatments for conditions ranging from severe burns to Legionnaires Disease.

Water Purification:

Silver is employed as a bactericide and algaecide in an ever increasing number of water purification systems in hospitals, remote communities and, more recently, domestic households. Silver ions have been used to purify drinking water and swimming pool water for generations. New research into silver compounds is providing physicians with powerful, clinically effective treatments against which bacteria cannot develop resistance. An increasing trend is the millions of on-the-counter and under-the-counter water purifiers that are sold each year in the United States to rid drinking water of bacteria, chlorine, trihalomethanes, lead, particulates, and odor. Here silver is used to prevent the buildup of bacteria and algae in the filters. Of the billions of dollars spent yearly in the U.S. for drinking water purification systems, over half make advantageous use of the bactericidal properties of silver. New research has shown that the catalytic action of silver, in concert with oxygen, provides a powerful sanitizer, virtually eliminating the need for the use of corrosive chlorine.

Catalysts:

One of the great discoveries of chemistry was that the efficiency of chemical reactions can be significantly increased in the presence of other elements or compounds that do not enter into the reaction. A hundred years ago it was discovered that silver was one of those elements. Ever since, silver has been essential to the production of chemicals for the US $300 billion plastics industry. It is estimated that some 700 tons of silver are in continuous use in the world’s chemical industry for the production of two compounds essential to the plastics industry. One is the reaction that produces ethylene oxide (the basic building block for flexible plastics), the other is the reaction that produces formaldehyde (the building block of solid plastics). Since 1908, it has been known that silver greatly increases the efficiency of the production of formaldehyde from methyl (wood) alcohol. Here silver catalyses the oxidation of an alcohol into an aldehyde called formaldehyde, which is one of the most important industrial and research chemicals. It is an essential building block for a class of plastics with an estimated world production exceeding 15-million tons per year which includes adhesives, laminating resins for construction plywood and particle board, finishes for paper and electronic equipment textiles, surface coatings that resist heat and scratches, dinnerware and buttons, casings for appliances, handles and knobs, packaging materials, automotive parts, thermal and electrical insulating materials, toys, and the list goes on. Silver is the only catalyst that will oxidize ethylene gas into ethylene oxide whose worldwide production exceeds 14-million tons per year. It is the building block for polyester textiles used to make all types of clothing and a great variety of specialty fabrics, it is also used for molded items (such as insulating handles for stoves, key tops for computers, electrical control knobs, domestic appliance components, and electrical connector housings), and Mylar tape which makes up 100% of all audio, VCR, and other types of recording tapes. About 25% of ethylene oxide production is used to produce antifreeze coolant for automobiles and other types of vehicles. An additional 10% is used to produce cleaning and wetting agents, and the remaining 5% to make cleaning solvents. Oxidative Capacity – Silver is a recognized powerful oxidizer. Metallurgists have long known the unique affinity of silver with oxygen. Molten silver will hold ten times its volume in oxygen. On freezing, the contraction of silver vigorously ejects the oxygen; a dangerous activity known as spitting. Not all oxygen is ejected; much is retained in the silver lattice as well as adhered to its surface.

Atomic oxygen (O⁺²) fits within the silver lattice and as silver resists oxidation, it is an ideal atomic oxygen reservoir. As atomic oxygen (also called nascent oxygen) is extremely reactive, the silver is essentially a reservoir for oxidation reactions, wherein the oxygen is immediately available to react with any organic or inorganic compound it contacts. Silver can be oxidized chemically, but the oxygen is so weakly held that AgO or Ag₂O decomposes below 200°C. Furthermore, atomic oxygen adsorbed on the silver surface recombines to form molecular O₂ at about 300°C. [See: C.B. Wang, G. Deo and I.E. Wachs, “Interaction of Polycrystalline Silver with Oxygen, Water, Carbon Dioxide, Ethylene, and Methanol: In Situ Raman and Catalytic Studies,” Jour. of Physical Chemistry B, Vol. 103, p. 5645 (1999)].

The resistance of silver to oxidation is such that silver will not sustain combustion even if ignited [See: R.W. Monroe et al, “Metal Combustion in High-Pressure Flowing Oxygen,” Flammability and Sensitivity of Materials in Oxygen-Enriched Atmospheres, ASTM STP 812, Am. Soc, Testing Mats., Conshohocken, PA, (1983)].  Because the spaces in its crystal structure permit oxygen atom to flow, silver is used as a filter to separate it from other gases and provide an output of pure atomic oxygen for oxidation studies. [See: R.A. Outlaw, “O₂ and CO₂ Glow-Discharge-Assisted Oxygen Transport Through Ag,” Jour. Applied Physics, Vol. 68 (3), p. 1001-1004 (1 August 1990).]

Raman (infrared) spectroscopy and laser-equipped spectrometers have revealed the role silver plays in catalyzing oxidation reactions. In the catalytic reaction chamber, as air flows over pure silver crystals individual oxygen atoms (O⁺²) are adsorbed onto the silver surface. These highly charged (O⁺²) atoms aggressively react (oxidize) with any gaseous organic compounds flowing past. In the case of methyl alcohol (CH₃OH) (industrial wood alcohol), the atomic oxygen oxidizes the hydrogen atom from the -OH group to form water (H₂O) and with the hydrogen removed the compound becomes methyl oxide (CH₂O) (formaldehyde). A detailed analysis of these reactions is given in: [C.B. Wang, G. Deo and I.E. Wachs, “Interaction of Polycrystalline Silver with Oxygen, Water, Carbon Dioxide, Ethylene, and Methanol: In Situ Raman and Catalytic Studies,” Jour. of Physical Chemistry B, Vol. 103, p. 5645 (1999)].

Multiple Catalysts – The action of silver may be enhanced by the addition of other metals or compounds. For example, the combination of silver with certain alkali metal salts, such as CsCl, lowers the desorption energy of long chain olefins (e.g. CH₂=CH-CH₃) and by doing so permits removal of a hydrogen atom by oxidation without reducing the entire compound to CO₂ and H₂O. The catalytic conversion of butadiene and other hydrocarbons into their oxides by this technique is being used by the Eastman Chemical Company, Kingsport, TN, to provide chemicals not otherwise produced economically. [See: “The Selective Epoxidation of Non-Allylic Olefins Over Supported Silver Catalysts,” John Monnier, Studies on Surface Science, Catalysis, Vol. 110, pp. 135-149 (1997), 3rd World Congress on Oxidation Catalysis, (1997)]. Additional catalysts downstream can enhance the overall efficiency of silver. For example: in current practice, a stream of gaseous methanol (wood alcohol) over silver crystals results in 90% conversion to formaldehyde. By conducting the output stream over an additional bed of copper crystals, much of the remaining methanol can be converted bringing the total conversion to better than 93%. This might appear to be a small addition, but considering the amounts involved (15 million tons per year) it is economically significant as the combination provides a higher purity formaldehyde requiring less intensive purification. [See: Formaldehyde Production, U.S Patent, No. 6,147,263, Nov. 14, 2000, I. E. Wachs, Lehigh University, Bethlehem, PA].

The oxidizing power of silver clearly has wide application. An interesting example is the application of silver catalysts to convert waste gas from Kraft pulp mill operations into valuable industrial chemicals. Emissions from Kraft pulp mills are largely methanol with some organic sulfides and a smaller amount of terpenes (long chain hydrocarbons). Instead of burning this gas, sorptive resins and molecular sieves capture the terpenes, and the silver catalyst converts the methanol, dimethyl sulfide and other sulfur compounds into formaldehyde, which is treated to reduce acidity to commercial levels, then transported to consumers providing a positive income stream to the mill. [See: Treating Methanol-Containing Waste Gas Streams, U.S. Patent 5,907,066, May 25, 1999, and Production of Formaldehyde from Methyl Mercaptans, U.S. Patent 5,9969.191, October 19, 1999, I.E. Wachs, Lehigh University, Bethlehem, PA].

Liquid Phase Catalysis – In contrast to the industrial use of silver catalysts in gaseous phase reactions (as above), silver is equally effective as an oxidant in aqueous phase reactions. For the Nature2^TM canister [see: www.Nature2.com], silver is deposited as microcrystals on an aluminum oxide (alumina) support in a canister through which water is conducted. Here silver provides an extremely active reaction chamber where bacteria, viruses, or other organic material are oxidized to destruction. Additionally, certain inorganic materials in the stream passing over the silver-alumina are oxidized to form relatively stable oxygen-rich compounds, which continue to sanitize the water downstream. Tests have demonstrated an instantaneous 99% kill rate for bacteria, with complete removal of E. coli (a fecal pollutant) within a 2.0 to 2.5 seconds contact time. The addition of ozone into the input stream powerfully increases the oxidative capacity of the canister. Studies reveal its efficacy to purify drinking, agricultural, and food process water, as well as treatment of wastewater. Silver Catalyst Manufacturers – Academy Corp., Albuquerque, NM (505-345-1805) Degussa, Hanau, Germany (011-49-6181-59-5770) W.C. Heraeus, gmbh, Hanau, Germany (011-49-6181-35-4833) Scientific Design, Inc., Little Ferry, NJ (201-641-0500) (ethylene oxidation only) Stonehart Associates, Madison, CT (203-245-7507) (silver-plated carriers only). Tanaka Kikinzoku, Indianapolis, IN (317-598-0796).