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.
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.
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
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.
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 Nature2TM 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).
- Water Science and Technology 31:5-6 (1995) 123-129 – Rami Pedahzur et al. – The interaction of silver ions and hydrogen peroxide in the inactivation of E. coli: a preliminary evaluation of a new long acting residual drinking water disinfectant
- Water Science and Technology 31:5-6 (1995) 119-122 – J. M. Cassells et al. – Efficacy of a combined system of copper and silver and free chlorine for inactivation of Naegleria fowleri amoebas in water
- Water Science and Technology 35:11-12 (1997) 87-93 – R. Pedahzur et al. – Silver and hydrogen peroxide as potential drinking water disinfectants: their bactericidal effects and possible modes of action
- Water Science & Technology 42:1-2 (2000) 293-298 – R Pedahzur et al. – The efficacy of long-lasting residual drinking water disinfectantsbased on hydrogen peroxide and silver
- Water Science & Technology 42:1-2 (2000) 215-220 – L Liberti et al. – Comparison of advanced disinfecting methods for municipal waste water reuse in agriculture
- Accumulation of copper and silver onto cell body of and its effect on the inactivation of Pseudomonas aeruginosa
- J Water Health – (2006) – David Collart et al. – Efficacy of oligodynamic metals in the control of bacteria growth in humidifier water tanks and mist droplets
- Silver Institute at www.silverinstitute.org
- http://www.silver-colloids.com/Papers/IonsAtoms&ChargedParticles.PDF Ions are positive, particles are negatively charged.