Scavenger

== Description ==
Any substance that actively absorbs or consumes unwanted impurities and pollutants in a system. For example, vapor phase inhibitors are used to scavenge hydrogen sulfide before it can tarnish silver. 
Test results from Schieweck (2020) show that both under active and passive conditions (with/without forced air exchange), pure and impregnated activated carbons have the best adsorption efficiency for substances often detected in museum environments, such as emissions from construction and furnishing materials. However, even under under active conditions, charcoal cloths/foams and zeolites, often specially designed for museum purposes, showed a low adsorption efficiency and exhibit breakthrough after only a short time. Silica gels, often installed to buffer RH were not shown to be effective VOC sorbents.
See also hydrogen sulfide scavenger, oxygen scavenger and desiccant.
Table for selected sorbents.
Sorbent 	Types 	Form/Examples 	Uses 	Drawbacks
Pure charcoal 	* Activated carbon, extra-fine pores * Activated carbon, high inner surface * Granulated activated carbon (GAC) 	black powder, beads or pellets 	A catchall sorbent that removes small hydrocarbons, chlorine, nitrogen oxides, and VOCs (including organic carbonyls); physically adsorbs on inner surface; used in HVAC systems to filter gaseous pollutants; pore size determines sorption capacity 	Difficult to determine when exhausted; may be regenerated (by baking in high-temperature oven with vent) or replaced; in some countries, used carbon is classified as a hazardous waste material making disposal costly; when exposed to high humidity (rain), water or water vapor vapor can replace organic compounds adsorbed within the pores of the carbon thus releasing VOCs into the environment; small molecules not as effectively adsorped as large molecules
Impregnated charcoal 	* GAC mixed with a base (NAOH, KOH) * GAC mixed with oxidizer (FeOH, KI, KMnO4) * GAC mixed with activated alumina impregnated with KOH or KMn04 	black or gray irregular pellets 	As above, removes hydrocarbons, VOCs, and NO2 with additional removal of sulfur dioxide, hydrogen sulfide, amines, and organic acids; permanganate is an indicator wthat is purple when fresh and brown when spent. 	Avoid direct contact with impregnated materials; Can only be regenerated as activated carbon without impregnated chemical(s)
Charcoal cloth 	* Activated carbon between two layers of polyester non-woven cloth* Composite carbon filter media fabric* Activated carbon felt, fiber structure* Open-cell polyurethane foam coated with activated carbon granules	soft fabric , pillow or shaped filter ([ https://flexzorb.com/ Flexzorb])	Useful in microenvironments with low-level emissions; eliminates same gases as activated charcoal; good mitigation treatment for display cases and storage cabinets; easy to use; durable; does not shed carbon particles 	Small reserve of carbon to adsorb pollutants; short longevity, thus requires frequent replacement; cannot be regenerated.
Activated alumina with potassium permanganate 	* Available in different pore sizes 	purple pellets (Purafil); filters 	Spherical, porous pellets remove gaseous pollutants from the air through chemisorption; harmful gases from the air into harmless materials that are irereversibly trapped inside the pellet; targets the removal of hydrogen sulfide (H2S), sulfur dioxide (SO2), nitric oxide (NO), and formaldehyde (CH2O).	
Molecular sieves and Zeolites 	* Available in different pore sizes 	white powder, sticks, granules 	Naturally adsorbs water and small volatile compounds; high sorption capacity; selection of compounds is directly related to pore size volume; may be regenerated with heat; best used for aliphatic and aromatic hydrocarbons 	Does not work well for polar materials, such as acids or amines; tends to be more expensive and difficult to obtain; are not as efficient as activated carbon.
Silica gel 	* Available with Lithium chloride or Al2O3 	White powder or pellets, often in packages 	Adsorb small amounts of VOCs; best for polar molecules, such as alcohols and amines 	Water molecules can replace absorbed organics; degraded by acid compounds
Foam or fabric embedded with silver or copper	cotton or polyester felted acrylic cloth impregnated with finely ground silver or copper 	(Corrosion Intercept, Pacific Silvercloth) 	Reduces contaminants that can tarnish metals (SO2, H2S and acids); acts as a sacrificial surface to rapidly remove reduced sulfides before they can reach silver objects; cloth can be glued to drawers or cabinet walls or ordered as bags to hold silver objects. 	Limited lifetime, although the cloth can be effective for several decades, depending on the environment where the silver is stored. Cannot be regenerated.
Acid-free cardboard embedded with zeolites 	 	 	Acid-free, durable, absorbs and neutralizes pollutants; best used for solvents and plasticizers 	Cannot be regenerated.
Oxides 	* Zinc oxide catalyst * Charcoal impregnated with oxides 	 	Oxides irreversibly capture pollutants via reactions or chemisorption; designed to targed inorganic gases (HCN, H2S, ammonia, acids, amines, phosphine and arsine) 	Cannot be regenerated.
== Synonyms and Related Terms ==
getter; pollutant absorber; vapor phase corrosion inhibitor; activated charcoal; activated carbon; charcoal cloth; 
Brand names: Purafil; Puracarb; Pacific silvercloth; Ageless®; Scavengel [Art Preservation Services]
==Resources and Citations==
* Schieweck, A. "Adsorbent media for the sustainable removal of organic air pollutants from museum display cases". Herit Sci 8, 12 (2020). Link
* Cecily Grzywacz, "Monitoring for Gaseous Pollutants in Museums", Getty Publications, 2006.
* AIC Conservation Wiki: Exhibit Technical Notes: Environmental Control
* Exhibit Guidelines Technical Note: Using Pollutant Absorbers Inside an Exhibit Case
* Delaney P, Healy RM, Hanrahan JP, Gibson LT, Wenger JC, Morris MA, Holmes JD. "Porous silica spheres as indoor air pollutant scavengers", J Environ Monit. 2010 Dec; 12(12):2244-51. Link
* Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
* Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002
* Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
* The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
Category:Materials databaseCategory: MWGCategory: Climate/EnvironmentCategory: Comparisons