16 Environmental Applications

Environmental applications are applications that pertain to protecting the environment from pollution. The protection can involve the removal of a pollutant or the reduction in the amount of pollutant generated. Pollutant removal can be attained by extraction through adsorption on the surface of a solid (e.g., activated carbon) with surface porosity. It can also be attained by planting trees, which take in CO2 gas. Pollutant generation can be reduced by changing the materials and/or processes used in industry by using biodegradable materials (materials that can be degraded by Nature so that their disposal is not necessary), by using materials that can be recycled, or by changing the energy source from fossil fuels to batteries, fuel cells, solar cells, and/or hydrogen.

Materials have been developed mainly for structural, electronic, thermal, or other applications without much consideration of disposal or recycling problems. It is now recognized that such considerations must be included during the design and development of materials rather than after the materials have been developed.

Materials for adsorption are central to the development of materials for environmental applications. They include carbons, zeolites, aerogels, and other porous materials. Desirable qualities include large adsorption capacity, pore size large enough for relatively large molecules and ions to lodge in, ability to be regenerated or cleaned after use, fluid dynamics for fast movement of the fluid from which the pollutant is to be removed, and, in some cases, selective adsorption of certain species.

Activated carbon fibers are superior to activated carbon particles in fluid dynamics due to the channels between the fibers. However, they are much more expensive.

Pores on the surface of a material must be accessible from the outside in order to serve as adsorption sites. In general, the pores can be macropores (> 500 A), mesopores (between 20 and 500 A), micropores (between 8 and 20 A), or micro-micropores (less than 8 A). Activated carbons typically have micropores and micro-micropores.

Electronic pollution is an environmental problem that has begun to be important. It arises from the electromagnetic waves (particularly radio waves) that are present in the environment due to radiation sources such as cellular telephones. Such radiation can interfere with digital electronics such as computers, thereby causing hazards and affecting society's operation. To alleviate this problem, radiation sources and electronics are shielded by materials that reflect and/or absorb radiation. Chapter 4 addresses shielding materials.

0 0

Post a comment