esm223 18 Nanomaterials

esm223 18 Nanomaterials - Nanomaterials: New Emerging...

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Nanomaterials: New Emerging Contaminants and Their Potential Impact to Water Resources By William E. Motzer Introduction Manufactured nanomaterials (MNMs) are a relatively new class of elemental metals, chemical compounds, and engineered materials with particle sizes in the nanometer (nm) range (1 x 10 –9 m to 100 x 10 9 m). In comparison, a human hair is 80,000 nm in diameter, a red blood cell is about 7,000 nm wide, DNA is about 2 to12 nm in width, and a water molecule is approximately 0.3 nm across. This “nanoworld” now includes several different substance classes, including: (1) Carbon-based materials and structures such as C 60 fullerene, which can be formed into carbon nanotubes. (2) Metal-based substances such as nanogold, nanosilver, and nanometal oxides such as titanium oxide. These also include quantum dots, which are packed semiconductor crystals whose optical properties can change with size; they also have the ability to absorb light and re-emit it in different colors depending on the nanocrystal’s size. (3) Dendrimers are polymers constructed from branched units. A dendrimer’s surface has numerous chain ends that can be designed to perform specific chemical functions. Also, dendrimers generally are hollow spheres into which other molecules or atoms can be placed. This makes them useful for drug delivery. (4) Bio-inorganic composites, such as titanium with attached DNA strands. These can be used to treat disease (Royal Academy, 2004; Elder, 2006; U.S. EPA, 2007). Several classes of MNMs are now globally manufactured in hundred to thousands of metric tons per year. These include MNMs for structural applications (ceramics, catalysts, films and coatings, and composite metals), skin care products (metal oxides), information and communication technologies (nanoelectronic and optoelectronic materials, organic light emitters, and nanophosphors), biotechnology (drug delivery, diagnostic markers, and biosensors) and environmental technologies (nanofiltration and membranes) (Borm and others, 2006).
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Characteristics The unique size of MNMs means that, in some ways, they will behave as new chemical substances (Borm and others, 2006). Two main factors distinguish MNM properties from ordinary materials (DTSC, 2007; Nel, 2007): (1) They have relatively large surface areas when compared to the same mass of material produced in larger form. For example, a 1.0 cm cube has a surface area of 6 cm 2 . This same cube separated into 1.0 mm cubes now has a surface area of 60 cm 2 ; but if further divided into 1.0 nm cubes, the total surface area becomes 60 x 10 6 cm 2 . This may cause the substance to become more chemically reactive; substances that were inert in large- scale form can become reactive in nanoscale form. Size reduction may also affect the material’s strength. (2) Quantum effects can begin dominating MNMs, particularly at the lower end of the
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esm223 18 Nanomaterials - Nanomaterials: New Emerging...

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