SI Prefixes in the Environment

CoreChem: SI Prefixes The SI base units are not always of convenient size for a particular measurement. For example, the meter would be too big for reporting the thickness of this page, but rather small for the distance from Chicago to Detroit. To overcome this obstacle the SI includes a series of prefixes, each of which represents a power of 10. These allow us to reduce or enlarge the SI base units to convenient sizes. The figures below show how these prefixes can be applied to the meter to cover almost the entire range of lengths we might wish to measure. Prefixes Used for Decimal Fractions and Multiples of SI Units.

One non-SI unit of length, the angstrom (Å), is convenient for chemists and will continue to be used for a limited time. Since 1Å = 10–10 m, the angstrom corresponds roughly to the diameters of atoms and small molecules. Such dimensions are also conveniently expressed in picometers, 1 pm = 10–12 m = 0.01Å, but the angstrom is widely used and very familiar. Therefore we will usually write atomic and molecular dimensions in both angstroms and picometers. The SI base unit of mass, the kilogram, is unusual because it already contains a prefix. The standard kilogram is a cylinder of corrosion-resistant platinum-iridium alloy which is kept at the International Bureau of Weights and Measures near Paris. The kilogram was chosen instead of a gram because the latter would have made an inconveniently small piece of platinum-iridium and would have been difficult to handle. Also, units of force, pressure, energy, and power have been derived using the kilogram instead of the gram.

The magnitudes of some distances and lengths in the range 1018 through 10–18 m, expressed in SI units.

Despite the fact that the kilogram is the SI unit of mass, the standard prefixes are applied to the gram when larger or smaller mass units are needed. For example, the quantity 106 kg (1 million kilograms) can be written as 1 Gg (gigagram) but not as 1 Mkg (megakilogram). The operative rule here is that one and only one prefix should be attached to the name for a unit. Figure 1.6 illustrates the use of this rule in expressing the wide range of masses available in the universe. Note that the masses of atoms and molecules are usually so small that scientific notation must be used instead of prefixes.

The masses of some objects in the range 1018 through 10–27 g, expressed in SI units. Retrieved from "wiki.chemprime.chemeddl.org/i...em:SI_Prefixes"

Nanoparticles for environmental remediation

Nano is the Greek for “dwarf” which means one billionth (1). A human hair is approximately 75,000 nm across (1). The National Nanotechnology Initiative states that:

1. Nanotechnology involves research and technology development at the 1nm-100nm range. 2. Nanotechnology creates and uses structures that have novel properties because of their small size. 3. Nanotechnology builds on the ability to control or manipulate at the atomic scale. (1)

At the nanoscale, the interactions and physics between atoms display exotic properties that they don’t at larger scales (1). Nanoscale materials have found application in a variety of areas within scientific, environmental, industrial, and medical areas (2).

The U.S. Environmental Protection Agency (EPA) has a list of more than 1500 Superfund Sites across the nation. A Superfund site is “an uncontrolled or abandoned place where hazardous waste is located, possibly affecting local ecosystems or people” (3). Various remediation technologies exist to assist in the cleaning up of these sites. Of these, approximately 71 sites are using or testing nanoparticles for remediation (4).

Nanoscale materials have been used to remediate contaminated soil and groundwater at hazardous waste sites, such as sites contaminated by chlorinated solvents or oil spills (5).

Nanoscale materials are particularly useful for environmental applications because of their large surface area to volume ratio (5). The large surface area allows for more contaminants to adsorb onto the surface of the nanoscale material and interact with it. Greater interaction with the nanoscale materials results in a rapid reduction of contaminant concentrations (5). In addition, because of their small size, nanoscale materials are able to pass through very small spaces below the ground (5). When they are coated with the right material, the nanoscale materials can also remain suspended in the ground water which leads to continued interaction with contaminants (5).

Figure \(\PageIndex{1}\). Micrograph of a nanowire curled into a loop in front of a strand of human hair. The nanowires can be as slender as 50 nanometers in width, about one-thousandth the width of a hair. A nanometer is one billionth of a meter – about one ten-thousandth the thickness of a human hair. Credit: Limin Tong/Harvard University (6)

Nanoscale materials containing iron have been the most widely used nanoscale materials in full-scale applications for site remediation (2). One common approach is to build a conventional iron wall, which is composed of a mixture of granular iron nanoparticles and sand. The contaminated ground water flows through the wall, and as it passes through, the nanoparticles remove the contaminants, yielding cleaner water on the other side (7).

Figure \(\PageIndex{2}\). Nanoscale materials that contain iron are the most widely used nanoscale materials in full-scale applications for site remediation.

Figure \(\PageIndex{3}\). Permeable reactive barrier” made with millimeter-sized grade granular iron (7)

Sources:

1) Booker, Richard and Boysen, Earl. Nanotechnology for Dummies. Wiley 2005. http://books.google.com/books?id=dPzDkOaVIxgC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

2) Nanotechnology: Applications for Environmental Remediation CLU-IN Technology Focus Area Fact Sheet. US EPA. www.clu-in.org/download/remed...sheet-2011.pdf

3) “Superfund Sites Where You Live” US EPA. http://www.epa.gov/superfund/sites/

4) “US EPA OSWER Selected Sites Using or Testing Nanoparticles for Remediation” www.clu-in.org/download/remed...-site-list.pdf

5) “Nanotechnology: Applications for Environmental Remediation Overview” US EPA

http://www.clu-in.org/techfocus/default.focus/sec/Nanotechnology%3A_Applications_for_Environmental_Remediation/cat/Overview/

6) “Researchers Develop Nanoscale Fibers that are Thinner than the Wavelengths of Light they Carry” NSF Office of Legislative and Public Affairs.

http://www.nsf.gov/od/lpa/news/03/pr03147.htm

7) “Zero-Valent Iron (ZVI)” Center for Groundwater Research. cgr.ebs.ogi.edu/iron/#results

From ChemPRIME: 1.4: SI Prefixes

Contributors and Attributions

• Ed Vitz (Kutztown University), John W. Moore (UW-Madison), Justin Shorb (Hope College), Xavier Prat-Resina (University of Minnesota Rochester), Tim Wendorff, and Adam Hahn.